STUDIES IN PHYSIOLOGY ANATOMY AND HYGIENE STUDIES IN PHYSIOLOGY ANATOMY AND HYGIENE BY JAMES EDWARD PEABODY, A.M. INSTRUCTOR IN BIOLOGY IN THE MORRIS HIGH SCHOOL. NEW YORK CITT ILLUSTRATED Nefo gorfc THE MACMILLAN COMPANY LONDON: MACMILLAN & CO., LTD. 1912 All rights reserved BIOLOGY LIBRARY G COPYRIGHT, 1903, 1907, BY THE MACMILLAN COMPANY. Set up and electrotyped. Published July, 1903. Reprinted February, July, 1905 ; July, 1906. New edition, May, 1907; April, 1908; February, August, 1909; January, 1910 ; March, December, 1911; September, 1912. PKEFACE IN the preparation of this book an attempt has been made to combine the following features : — (1) As the title-page implies, emphasis is constantly laid on physiology, and anatomical details are given only so far as is necessary to make intelligible the various physiological processes. Hygiene is discussed in a separate section at the end of the study of each system ; for, while believing that the lessons of hygiene are of primary importance, the author is confident that a youth will learn these lessons best by getting some comprehension of the normal action of his various organs. (2) An experience of ten years in teaching physiology to high school pupils has demonstrated that laboratory work on the part of the pupil is by far the most satisfactory method of presenting this subject. While this book is not a laboratory guide, it is intended to lead the pupil to study the organs and tissues of his own body or those of other animals rather than to learn text-book statements about them. Experiments and demonstrations should, therefore, precede the study of a given topic in the text-book. (See Peabody's "Laboratory Exercises in Anatomy and Physi- ology." Henry Holt & Co., New York City.) ' (3) Physiological processes can never be understood by pupils unless they are taught at least some of the simpler principles of chemistry. For this reason the early chapters of the book are devoted to a discussion of the common elements and their compounds, to atmospheric pressure, oxidation, and neutralization. 304679 Vl PREFACE (4) In the course of study prescribed in New York City for first-year biology, physiology is taught in connection with botany and zoology. This has been found to be a most fortunate arrangement, for the pupil is easily interested to consider physiological processes from a comparative stand- point. Because of the interest added thereby to the subject, there have been inserted in the book several sections on the physiology of some of our common animals and plants. (5) Since pupils sometimes get an impression that the facts of physiology have always been known, the historical development of the subject has been frequently referred to ; some of the mistakes made by early physiologists have been pointed out ; and the pupil is led to appreciate the fact that a great many biological problems are still unsolved. (6) Throughout the book, unless common names fail to give sufficient precision, scientific terminology has been avoided. Whenever technical terms are used, their division into syllables is given, and their Latin and Greek deriva- tions are noted. (7) In all States of the Union but two the statute law prescribes that a certain amount of instruction shall be given regarding the effects of alcohol and narcotics. To fulfill the requirements of these laws twenty pages relating to this subject have been inserted. In this connection extensive quotations have been made from the most recent report of the Committee of Fifty, on the "Physiological Aspects of the Liquor Problem." This non-partisan com- mittee, composed of men eminent in science and education, has been working on this problem for nearly ten years. Their conclusions have, therefore, great weight of authority. (8) And, finally, while it cannot be hoped that this book is entirely free from errors, I have used every means at hand to secure this end, and I wish to express my deep indebtedness to my friends for their suggestions and criti- cisms. The manuscript was carefully read by Miss Martha F. Goddard of the Department of Biology, Morris High PREFACE vii School. Especially valuable criticism has been given too by Mr. Harold E. Foster of the English Department of the Morris High School, and by Dr. F. C. Waite of the Western Eeserve Medical School, Cleveland, Ohio. I am also in- debted for suggestions to Dr. Frank Rollins of the Depart- ment of Physics, to Mr. Sanford L. Cutler of the Classical Department, and to Mr. J. M. Johnson and other members of the Department of Biology of the Morris High School. In preparing the chapter on foods I have received much assistance from a leading investigator on foods and nutri- tion. Dr. T. Mitchell Prudden of the College of Physicians and Surgeons has made valuable suggestions for the sec- tions relating to bacteria, and Dr. 0. S. Strong of Columbia University has read and criticised the chapter on the ner- vous system. In 1898 the New York State Science Teach- ers' Association appointed a Committee of Five, of which the author is a member, to find out what is known in regard to the effects of alcohol and narcotics on the human body. To the other members of this committee I am indebted for help in writing the sections relating to alcohol and nar- cotics. J. B. P. THE MORRIS HIGH SCHOOL, June 15, 1903. CONTENTS CHAPTER I INTRODUCTION PAGE The Study of an Engine — The Study of the Human Body — Anatomy — Physiology — Hygiene — Biology — The Kela- tion of Physics and Chemistry to Physiology ... 1 CHAPTER II LESSONS IN CHEMISTRY 1. THE STUDY OF A MATCH : Phosphorus — Oxid of Phosphorus — Sulphur and Oxid of Sulphur — Water — Carbon and Carbon Dioxid — Test for Carbon Dioxid — Mineral Sub- stances — Definitions — Elements — Compounds — Oxida- tion— Summary ......... 5 2. A STUDY OF AIR : Preparation of Oxygen — Atmospheric Pressure — Collection of Oxygen — Physical Properties of Oxygen — Chemical Properties of Oxygen — Preparation of Nitrogen — A Test for Acids — The Composition of Air — Properties of Nitrogen — Summary .... 11 3. THE CHEMICAL COMPOSITION OF THE HUMAN BODY: Water — Mineral Matters — Gases — Fats — Carbohydrates — Nitrogenous Substances — Summary . . . . .16 CHAPTER III A STUDY OF LIVING SUBSTANCE 1. THE GENERAL STRUCTURE OF ANIMAL BODIES : Vertebrates and Invertebrates — Regions of the Body — Organs — Tissues 20 2. CELLS, THE UNITS OF LIVING SUBSTANCE : The Amoeba — Structure of a Cell — Cells of the Blood — Cells in Other Tissues — Intercellular Substance — Definition of a Tissue . 23 ix X CONTENTS PAGK 3. SOME OP THE PROPERTIES OF PROTOPLASM : Microscopic Appearance — Chemical Composition — Production of Energy — Growth — Repair — Cell Division ... 28 4. A STUDY OP BACTERIA : Changes caused by Bacteria — Microscopic Appearance of Bacteria — Size of Bacteria — Reproduction of Bacteria — Necessary Conditions for the Growth of Bacteria 32 5. A STUDY OP YEAST AND FERMENTATION: Changes caused by Yeast — Distillation — Fermentation — Microscopic Ap- pearance of Yeast — Reproduction of Yeast — Spore Forma- tion— Uses of Yeast — Patent Medicines .... 35 SUMMARIES : The Structure of the Living Human Body — The Functions carried on by All Protoplasm .... 39 CHAPTER IV A STUDY OF FOODS Why Foods are needed in the Body — Definition of Food . 41 1. THE COMPOSITION OF FOODS: Nutrients — Refuse — Expla- nation of Food-Chart — Percentage of Nutrients in Foods 41 2. TEST FOR THE NUTRIENTS : Test for Proteids — Test for Fats — Test for Starch — Test for Grape Sugar — Test for Mineral Matters — Test for Water — Pure Food Laws. . 44 3. How PLANTS MANUFACTURE FOOD MATERIALS : Carbohydrates — Organs of a Plant — Starch Manufacture — Storage of Starch and Sugar — Proteid Manufacture .... 47 4. USES OF THE NUTRIENTS : — Uses of Proteids — Uses of Fats and Carbohydrates — Comparison of the Uses of the Nutri- ents — The Relative Fuel Value of the Nutrients — Uses of Mineral Matters and Water 50 5. COOKING OF FOODS : Importance of Proper Cooking — Meth- ods of cooking Meats — Reasons for cooking Meats — Soups — Boiling Meats — Stewing — Roasting and Broiling — Rea- sons for cooking Vegetables — Boiling Vegetables — Bread Making 52 6. DAILY DIET: Diet required by Americans — Necessity for a Mixed Diet 56 7. FOOD ECONOMY : Importance of Food Economy — Economy in the Purchase of Food — Waste of Food .... 57 SUMMARY : Review of Foods . . 60 CONTENTS xi CHAPTER V A STUDY OF STIMULANTS, NARCOTICS, AND POISONS PAGB 1. DEFINITION OF STIMULANT, NARCOTIC, AND POISON: Defini- tion of a Stimulant — Definition of a Narcotic ... 62 2. TEA AND COFFEE : Use and Abuse of Tea — Use and Abuse of Coffee 63 3. TOBACCO: Effect of Tobacco on Growth — Tobacco and Athletics 64 4. ALCOHOL : Alcohol as a Possible Food — Alcohol as a Stimu- lant, a Narcotic, and a Poison — Business Argument for Total Abstinence — Total Abstinence and Life Insurance — The Effect upon Dogs of Moderate Drinking of Alcohol . . 66 CHAPTER VI A STUDY OF BLOOD MANUFACTURE Definition of Digestion — Parts of the Alimentary Canal — Diges- tive Glands 75 1. THE MOUTH CAVITY: Walls of the Mouth Cavity — Mucous Membrane .......... 77 2. THE TEETH : Arrangement of the Teeth — Kinds of Teeth — Dental Formula — Milk Teeth — Structure of Teeth . 77 3. THE TONGUE : Structure of the Tongue — Functions of the Tongue 81 4. THE SALIVARY GLANDS : Position and Action of the Salivary Glands — Microscopical Structure of the Salivary Glands — Uses of Saliva 82 5. THE THROAT CAVITY: The Uvula — The Air Passages and the Epiglottis — Breathing and Swallowing — The Eusta- chian Tubes — The Process of Swallowing . . .84 6. THE ESOPHAGUS — Structure of the Esophagus — Function of the Esophagus 87 7. THE STOMACH: Position, Shape, Size — The Mucous Lining and Gastric Glands — Blood Supply of the Stomach — Muscles of the Stomach — Digestion in the Stomach — Digestion of Proteids 88 8. THE SMALL INTESTINE: Position and Shape — Peritoneum — Functions of the Small Intestine — Adaptations for Ab- sorption — The Villi 92 9. THE LARGE INTESTINE : Position, Form, Size — Ileo-caecal Valve — Vermiform Appendix 96 10. THE PANCREAS : Position, Form, Size — Structure of the Pancreas — Functions of the Pancreatic Juice — Digestion of Fats 97 xii CONTENTS PAGE 11. THE LIVER: Position, Form, Size — Functions of the Liver — Functions of the Bile 98 12. ABSORPTION FROM THE ALIMENTARY CANAL : Necessity for Absorption — The Principles of Osmosis — Law of Osmosis — Application of the Principles of Osmosis to Absorption — Absorption in Mouth, Throat, and Gullet — Absorption in the Stomach — Absorption in the Small Intestine — Ab- sorption in the Large Intestine „ 101 13. SYNOPSIS OF DIGESTION 105 14. THE HYGIENE OF DIGESTION : Importance of Subject — Hygienic Habits of Eating — Care of the Teeth — Adapta- tion of Foods to Individual Needs — Prevention of Consti- pation— The Use of Patent Medicines — Effects of Alcoholic Drinks on the Organs of Digestion 106 15. A COMPARATIVE STUDY OF DIGESTION : A Study of Teeth — The Tongue in Other Animals — The Alimentary Canal of the Earthworm — The Alimentary Canal of the Frog — The Alimentary Canal of the Pigeon — The Alimentary Canal of the Sheep — Comparison of the Digestive Organs Studied . . .109 CHAPTER VII A STUDY OF THE BLOOD 1. USES OF THE BLOOD : Nutrition in the Amoeba — Nutrition in Man — Uses of the Blood 117 2. A STUDY OF BEEF-BLOOD: Preparation — Blood Clot — Blood Serum — Cause of Coagulation — Blood Fibrin — Defibri- nated Blood — Difference between Blood Plasma and Blood Serum — Composition of Blood Serum — Change in Blood on mixing with Oxygen . . . . . . .118 3. HUMAN BLOOD: Application of the Study of Beef-blood — Red Blood Corpuscles — White Corpuscles — Amount of Blood in the Body .121 4. THE HYGIENE OF THE BLOOD : Conditions affecting the Red Corpuscles — Conditions affecting the Serum . . . 123 5. A COMPARATIVE STUDY OF BLOOD : Animals without Blood — Color of the Blood — Temperature of the Blood — White Corpuscles — Red Corpuscles 125 6. SUMMARY : Chemical Composition of Blood .... 127 CONTENTS xiil CHAPTER VIII A STUDY OF THE CIRCULATION OF BLOOD PAGE Definition of the Circulation — Organs of Circulation . . . 129 1. THE HEART : Position, Shape, Size — The Pericardium — The Heart a Double Organ — The Cavities of the Right and Left Hearts — The Valves of the Right and Left Hearts — The Blood Vessels connected with the Right Heart — The Semilunar Valves — The Blood Vessels connected with the Left Heart— The Beat of the Heart — The Action of the Valves of the Heart — Sounds of the Heart — The Blood Supply for the Heart .129 2. THE BLOOD VESSELS: Position of Arteries and the Pulse — Structure of Arteries — Position of the Veins — The Struc- ture of Veins — Position of the Capillaries — Importance of the Capillaries — Structure of the Capillaries — Flow of Blood in the Web of a Frog's Foot — Absence of Pulse in Capillaries and Veins . . . . . . . . 137 3. THE CIRCULATION OF THE BLOOD : The Two So-called Sys- tems of Circulation — The Pulmonary Circulation — The Systemic Arteries — The Systemic Veins — The Portal System of Veins — The Circulation but a Single System — Changes in the Composition of Blood — Inappropriateness of the Terms "Arterial" and "Venous" — Regulation of the Blood Supply to the Various Organs .... 142 4. THE LYMPHATIC SYSTEM: The Lymph — Changes in the Lymph — The Lymphatics — The Lacteals . . . .148 5. HYGIENE OF THE CIRCULATORY SYSTEM : Effect of Heat and Cold on the Arteries — Colds and their Prevention — Effect of Exercise on the Heart — Effect of Exercise on the Size of the Blood Vessels — Treatment of Cuts and Bruises — Effect of Alcohol on Organs of Circulation .... 151 6. A COMPARATIVE STUDY OF THIS CIRCULATION: Circulation in the Earthworm — Circulation in the Fish — Circulation in the Frog — Circulation in the Reptiles — Circulation in the Birds and Mammals — Comparison of the Organs of Circulation Studied 154 XIV CONTENTS CHAPTER IX A STUDY OF THE SKELETON PAGE X-Ray Pictures — The Uses of the Bony Framework of the Body — Regions of the Skeleton 159 1. THE SKELETON OP THE ARMS AND LEGS : Bones of the Arm — Bones of the Leg . 160 2. THE SKELETON OF THE NECK AND TRUNK: The Spinal Column — The Structure of a Vertebra — The Structure of Atlas and Axis — Adaptations shown in the Spinal Column — The Ribs and Sternum — The Pectoral Girdle — The Pelvic Girdle 162 3. THE SKELETON OF THE HEAD : The Bones of the Cranium — The Bones of the Face — Adaptations shown in the Structure of the Skull 170 4. DIFFERENCES BETWEEN THE SKELETON OF A CHILD AND THAT OF AN ADULT : Differences in Composition — Differ- ences in the Skull — Differences in the Spinal Column — Differences in the Breastbone — Differences in the Bones of the Arm and of the Leg ....... 172 6. STRUCTURE OF BONES: Structure of a Rib — Structure of a Soup Bone — Advantages of Hollow Bones — Blood Supply in Bones — Classification of the Bones in the Human Skeleton 174 6. CHEMICAL COMPOSITION OF BONE : Effect of Burning Bones — Action of Acid on Bones — Nutritive Ingredients found in Bones 177 7. A STUDY OF JOINTS : Definition of a Joint — Structure of a Leg-joint of Lamb — Classification of Joints . . . 179 8. THE HYGIENE OF THE SKELETON: Food and the Skeleton — Effect of Pressure on Bones 182 9. ACCIDENTS TO THE SKELETON: Fractures — Dislocations — Sprains .184 10. A COMPARATIVE STUDY OF SKELETONS: Skeletons of In- vertebrates and of Vertebrates — Invertebrate Skeletons — Vertebrate Skeletons — Anterior Appendages of Mammals — Peculiarities of the Human Skeleton . • . . 186 CONTENTS XV CHAPTER X A STUDY OP THE MUSCLES PAGE Importance of Muscle Tissue — Kinds of Muscle . . . 193 1. THE VOLUNTARY MUSCLES : The Biceps Muscle — The Tri- ceps Muscle — Arrangement of Muscles in the Body — Structure of Voluntary Muscle — Blood Supply of Muscles — Nerve Supply to Muscles — Standing — Walking — Running 194 2. INVOLUNTARY MUSCLE: Nerve Control — Functions — Struc- ture of Involuntary Muscle — Heart Muscle . . . 201 3. THE HYGIENE OF MUSCLE : Necessary Conditions for Healthy Muscles — Food— Fresh Air— Exercise — Rest. . . 202 4. A CoaiPARATivE STUDY OF LOCOMOTION : Amoeba — Para- mecium — Earthworm — Locomotion in Water — Locomo- tion in the Air — Locomotion on Land . . . 205 CHAPTER XI A STUDY OF RESPIRATION 1. NECESSITY FOR RESPIRATION: Definitions — Necessity for In- spiration — Necessity for Expiration — Wastes given off by the Lungs , 209 2. THE ORGANS OF RESPIRATION : Course taken by the Air — The Nose Cavity — The Throat and Larynx — The Wind- pipe* and its Branches — The Lungs — Blood Supply — The Pleura — The Structure of the Chest Cavity — Enlargement of the Chest Cavity — Movements of the Ribs — Structure and Movements of the Diaphragm — How the Lungs are filled with Air — Inspiration and Expiration . . . 210 3. CHANGES IN AIR AND BLOOD DUE TO RESPIRATION: Tem- perature of Inspired and of Expired Air — Composition of Inspired and of Expired Air — Changes in the Blood while passing through the Lungs 221 4. HYGIENE OF THE RESPIRATORY ORGANS : Hygienic Habits of Breathing — Effect of Exercise on Respiration — Effect of Tight Clothing upon Respiration — Diseases of the Respiratory Organs — Coughing, Sneezing, Choking — Suf- focation — Necessity of Ventilation — Methods of Ventila- tion — Proper Methods of Sweeping and Dusting . . 222 xvi CONTENTS PAGE 5. A COMPARATIVE STUDY OF RESPIRATION : Respiration in Single-celled Animals — Respiration in the Earthworm — Respiration in Fishes — Respiration in Air-breathing Ani- mals— Comparison of the Organs of Respiration Studied . 229 CHAPTER XII A STUDY OF THE SKIN AND THE KIDNEYS Characteristics of the Skin — Uses of the Skin .... 232 1. ANATOMY AND PHYSIOLOGY OF THE SKIN : Layers of the Skin — Characteristics of the Epidermis — Structure of the Epidermis — Structure of the Dennis — Nails — Hair — Glands of the Skin — Sebaceous Glands — Perspiratory Glands — Heat Regulation in the Body .... 233 2. HYGIENE OF THE SKIN: Importance of Bathing — Kinds of Baths — Care of the Hair — Care of the Nails — Treatment of Burns — Clothing — Effect of Alcohol on the Body Tem- perature .... 240 3. A COMPARATIVE STUDY OF THE SKIN : The Skin of Inverte- brates— The Skin of Amphibia — The Skin of Fishes and Reptiles — The Skin of Birds — The Skin of Mammals . 244 4. A STUDY OF THE SHEEP KIDNEY: General Appearance of the Kidney — Longitudinal Section of the Kidney . . 248 5. ANATOMY AND PHYSIOLOGY OF THE HUMAN KIDNEY : Posi- tion and Appearance — Microscopical Structure — Course taken by the Urine — Importance of the Kidneys — Blood Supply of the Kidneys . . ... . . .248 6. A COMPARISON OF EXCRETORY ORGANS: Secretion and Ex- cretion — The Kidneys and the Skin — The Lungs as Excretory Organs — The Liver as an Excretory Organ — The Kidneys of Vertebrates — The Kidneys of Invertebrates 251 CHAPTER XIII A STUDY OF THE NERVOUS SYSTEM The Body as a Collection of Organs — Cooperation of the Organs — Functions of the Nervous System — Parts of the Nervous System 253 1. ANATOMY OF THE SPINAL CORD: Shape and Size — Fissures — Coverings of the Cord — Cross Section of the Cord — Nerve Cells and Fibers 256 CONTENTS xvii PAGE 2. ANATOMY OP THE SPINAL NERVES : Number of Nerves — Distribution of Nerves — Origin of the Nerves — Structure of a Spinal Nerve — Structure of a Spinal Ganglion — Rela- tion of Cells and Fibers 260 3. PHYSIOLOGY OF THE SPINAL CORD AND THE SPINAL NERVES : Experiments on Animals — Functions of Nerve Fibers — Nerve Impulses — Reflex Action 263 4. THE SYMPATHETIC NERVOUS SYSTEM: Anatomy — Physiology 266 5. THE NERVOUS SYSTEM OF A FROG : Reason for Studying a Frog's Brain — Forebrain — Midbrain — Hindbrain — The Spinal and Sympathetic Nerve Systems — Summary — Frog Physiology — Functions of the Spinal Cord — Func- tions of the Hindbrain and Midbrain — Effect of remov- ing the Cerebral Hemispheres — Function of the Cerebral Hemispheres — Summary 268 6. ANATOMY OF THE HUMAN BRAIN : Protection for the Brain — Parts of the Brain — Hindbrain — Forebrain — Midbrain — Comparison of Human and Frog Brains — Section of Forebrain — Microscopic Structure of the Brain — Sensory and Motor Cells and Fibers — The Cranial Nerves . . 273 7. PHYSIOLOGY OF THE BRAIN: Reflex Activities — Conscious Activities — Localization of Functions in the Brain — Habitual Activities — Importance of Habit . . . .278 8. HYGIENE OF THE NERVOUS SYSTEM : Changes in the Nervous System during Life — Necessary Conditions for a Healthful Kervous System — Food and Air — Varied Activity — Rest — Effect of Alcohol on the Nervous System . . .283 9. A COMPARATIVE STUDY OF THE NERVOUS SYSTEM : Nerve Functions in Amoaba — The Nervous System of the Earth- worm— Nervous Functions in the Earthworm — The Nerv- ous System of Invertebrates and of Vertebrates — A Comparison of Vertebrate Brains 287 CHAPTER XIV A STUDY OF THE SENSES 1. THE SENSE OF TOUCH: The Sense Organs of Touch — Sen- sations of Touch 291 2. GENERAL SENSES: Sensations of Temperature — Sensations of Pain — Sensations of Hunger and Thirst . . . 293 XVlii CONTENTS PAGE 3. THE SENSE OF TASTE : Papillae of the Tongue -— The Taste Buds* — Sensations of Taste 294 4. THE SENSE or SMELL : The Nasal Cavities — The Sense Organs of Smell — Sensations of Smell . . . .296 5. THE SENSE OF SIGHT : Protection for the Eye — The Tear Glands and Ducts — Sebaceous Glands — Movements of the Eyes — General Form of the Eye — Coats of the Eye — The Lens of the Eye — The Humors of the Eye — The Eye as a Camera — Accommodation of the Eye — Sensations of Sight — The Blind Spot and the Yellow Spot — Defective Eyes — Hygiene of the Eyes 298 6. THE SENSE OF HEARING: The External Ear — The Middle Ear — The Bones of the Middle Ear — General Structure of the Inner Ear — The Structure and Functions of the Semi- circular Canals — The Structure and Functions of the Cochlea — Sensations of Sound — Loudness, Pitch, and Quality 308 CHAPTER XV A STUDY OF THE VOICE AND OF SPEECH The Vocal Organs of Man — The Cartilages of the Larynx — The Vocal Cords — Resonating Cavities — Speech — Loudness, Pitch, and Quality — The Care of the Voice — Sounds pro- duced by Other Animals . . . . . .315 INDIX • 321 STUDIES IN PHYSIOLOGY ANATOMY AND HYGIENE STUDIES IN PHYSIOLOGY ANATOMY AND HYGIENE CHAPTER I INTRODUCTION The Study of an Engine. — If we wished to make a careful and scientific study of a railroad locomotive, it would, per- haps, be best for us first to go to a machine shop where engines are built and repaired. There we could see the construction of each separate part and could also find how these various parts are put together to form a completed engine. But if we had never before seen an engine, the whole machine would probably have little meaning or interest for us until we had watched it in action. We should then learn how the locomotive is supplied with water and coal. We should see that the burning coal converts the water into steam, and that energy or power is thus furnished by which the pistons cause the drive wheels to revolve. All the pipes, cranks, levers, and rods we should find to be specially adapted for starting the locomotive, for keeping it in motion, or for stopping it. To understand thoroughly, however, the action of this complicated mechanism we should need to go still farther in our study. Considerable knowledge of the principles of levers would be required. We should have to investigate the processes involved in the burning of coal and in the change of water into steam, and we should seek an expla- B 1 2 STUD JE^ IN PHYSIOLOGY nation of the force exerted by the steam. In other words, the scientific student of an engine would necessarily study physics and chemistry, the sciences that lead to the solution of the problems just suggested. And finally, if we wished to become competent engineers, we should seek to acquire also the practical knowledge of how to get the most work out of a locomotive. We should study the best methods of feeding in the coal and of regulating the supply of water and of air; we should determine the amount of oil required, and the length of time the engine would run before needing a rest. Let us now summarize what we have learned thus far. An engine may be considered in at least three different ways. We may look at it as a collection of various pieces of iron and brass, and may devote our time to studying the form of the parts and the way they are put together. By watching the change of water into steam, and again by ob- serving the movement of wheels and levers, we may learn the uses of the parts. Or finally, we may study the machine with a view of determining the most successful methods of keeping it in good running order. The Study of the Human Body. — The human body, too, is a machine. But it is far more complicated than any loco- motive and capable of doing many more kinds of work. The body not only can move about and carry things from place to place, but it can also grow and repair itself, and within the body the mind can feel and think. Like the engine, however, it can be studied in three different ways. We may discuss its structure, its activities, and its proper care. When we are considering animal machines, these three branches of study are known respectively as a-nat'o-my, phys-i-ol'o-gy, and Jiy'gi-ene. Anatomy. — By the anatomy of an animal is meant the study of its structure. If one is considering the anatomy of the human body, for instance, one may discuss the form of the several parts, their microscopic structure, their positions INTRODUCTION 3 in the body, and the connections of these parts with each other. The anatomy of a lifeless body can be studied far more completely than can the anatomy of a living animal, for any complete knowledge of structure involves dissecting or cutting into the various regions. The term anatomy is derived from two Greek words which mean to cut up, (ana ' = up + tem'nein = to cut). Physiology. — For the study of physiology, however, a liv- ing organism is necessary, since this science is the study of the uses or functions of the various organs. The functions of a cat's claws can be determined only by watching the use the cat makes of them. Man has found out the use of the internal organs of animals largely by experimenting upon them, and many of the wonderful discoveries in medicine have been made by studying the physiology of dogs, guinea pigs, and other animals. Physiology has for most of us a meaning altogether too limited, for we usually confine the term to the study of the human body. We should remember that it includes the con- sideration of the functions not only of all the countless species of animals, but of all forms of plant life as well. And if we could carry our studies far enough, we should see that similar vital processes are performed in the lowest of plants and in the highest of animals, however much these organisms may differ in structure. Hygiene. — The word hygiene is derived from the Greek word hy-ge'ia, which means health. This branch of science treats of the conditions that tend to develop and maintain a healthy body. It cannot be studied to good advantage until one becomes acquainted with the structure and uses of the various parts of one's body ; it must, therefore, be pre- ceded by some knowledge of anatomy and physiology. Biology (Greek bi'os = life + log'os = science) is the gen- eral name given to the study of all living things. Hence this science treats of both animals and plants, and includes a consideration of their anatomy, physiology, and hygiene. 4 STUDIES IN PHYSIOLOGY The term biology is usually employed, however, when we are comparing the processes carried on in both of these two great kingdoms of animate bodies. If we confine our study to the structure and activities of plants alone, we call this part of the science botany. Zoology, on the other hand, treats of the anatomy and physiology of animals. Human physi- ology discusses man, the highest type of the animal king- dom ; hence it is a branch of the science of zoology, which in turn is one of the subdivisions of the study of biology. The Relation of Chemistry and Physics to Physiology We saw in a previous section that a complete explanation of the action of a locomotive requires some knowledge of physics and chemistry. This is far more true in animal physiology. We may study the various parts of the human body, and we may watch the activities of these parts, but we cannot begin to understand the processes that we see until we know some- thing of the chemical composition of lifeless as well as of living things, and something of the chemical changes that are constantly taking place all about us as well as within us. Our next chapter will therefore be devoted to a con- sideration of some simple experiments in chemistry. CHAPTER II LESSONS IN CHEMISTRY 1. THE STUDY OF A MATCH1 A SPLINTER of soft pine wood tipped with a mixture of phosphorus, sulphur, and other ingredients is one of the commonest necessities of every-day life. We light these matches a dozen times a day and throw them away half- burned, never thinking that we might learn from this ap- parently simple process many of the fundamental principles of chemical science. Phosphorus. — If in a dark room I draw the tip of a match across my finger, there is left behind a luminous streak. This is caused by the slow burning of phos'pho-rus. To understand what has taken place we must experiment with phosphorus alone. In its pure state it is a yellowish white, waxy solid. It is usually manufactured in sticks about the size of one's finger, and these, because of the great inflammability of phosphorus, are always kept under water. Suppose we cut off a bit of phosphorus about the size of a pea, and hold it on the knife tip.2 As it becomes dry it gives off little streams of white smoke, and the piece grad- ually diminishes in size. If it is rubbed vigorously against a rough surface, the waxy mass bursts into a bright yellow flame and soon disappears. Oxid of Phosphorus. — Let us now inquire somewhat closely into this process of burning. Our earth is sur- rounded by a mixture of gases that form the atmosphere. 1 See Peabody's "Laboratory Exercises," No. 1. Holt & Co. 2 Phosphorus should never be handled with the fingers. 5 6 STUDIES IN PHYSIOLOGY Close to the earth this air is comparatively dense. But if one could rise in a balloon from the surface, one would find that the air becomes more and more rare, and that it almost ceases to exist at a height of thirty to sixty miles. One of the constituents of the atmosphere is a gas called ox'y-gen. When we take the phosphorus from the water, we expose it to this omnipresent oxygen of the air. This is all that is necessary, for the mutual attraction between phosphorus and oxygen is so great that the two straightway combine to form a new substance. We saw the white fumes rising from the phosphorus and noticed that some of the latter disappeared. If we measured the exact amount of oxygen in the air before and after the experiment, we should find that small quantities of this gas also had disappeared. The white fumes are therefore formed by a chemical union of phosphorus with oxygen, and since the fumes are composed of these two substances alone, the new compound is called an oxid of phosphorus. Every time we draw a match across our fingers, we cause a little of the phosphorus to combine with surrounding oxy- gen, and we notice the peculiar smell of oxid of phosphorus. When we scratch the match more forcibly against a rough surface, we hasten this process by causing the heated phosphorus to combine rapidly with the oxygen gas of the air, and thus a flame is produced. In this chemical union both phosphorus and oxygen seem to disappear. They are not lost, however ; for on decomposing or analyz- ing the white fumes we find all of the phosphorus we had at first and all of the oxygen taken from the air. Sulphur and Oxid of Sulphur. — Let us light another match and continue our study. Soon after the white fumes of oxid of phosphorus begin to appear, we notice the suffocating odor of burning sulphur. The sulphur of commerce is usually obtained from mines near active or extinct vol- canoes and comes to us in the form of a yellow powder or of solid brimstone. If we treat a bit of it as we did the LESSONS IN CHEMISTRY 7 phosphorus, we are unable to make it burn, however vigor- ously we may rub it against a rough surface. When, how- ever, we touch a heated nail to the sulphur, the latter catches fire and burns with a pale blue flame, giving off the same suffocating smell that we perceived when the match head was aflame. In the burning of sulphur a process is going on similar to that already described in the case of phosphorus. The heated sulphur combines with a certain amount of the oxy- gen of the air, and an invisible gas is made which we recognize by its pungent odor. This new substance, being composed of sulphur and oxygen, is called oxid of sulphur. Our experiment teaches us that sulphur does not combine with oxygen as readily as does phosphorus, for the former could not be lighted by friction. The heat caused by the burning phosphorus on the match tip is sufficient, however, to set fire to the sulphur. Water. — We are now ready to study the composition of wood itself, and to note the changes that take place when it is burned. If we hold a lighted match stick just beneath the mouth of a dry tumbler, we soon notice that the inside of the glass is covered with a film of moisture. Water, then, is the first substance produced in the process of burn- ing wood.1 It goes into the air in the form of vapor and is then condensed by the cool surface of the glass. Carbon and Carbon Dioxid. — On extinguishing the flame of a burning match, we find that the wood has been converted into a black, brittle substance; this we call carbon. As was the case with sulphur, it is impossible to make the carbon burn by the heat of friction. If, however, we put the charred wood into a hot flame, the carbon catches fire, gradually disappears, and nothing remains but a powdery, gray ash. The same result is obtained if we allow a match to burn as long as it will, since the carbon is then heated red hot by the burning phosphorus and sulphur. In this 1 We shall prove later that water is an oxid of a gas called hydrogen. 8 STUDIES IN PHYSIOLOGY process the carbon takes to itself some of the oxygen about it and forms a colorless, tasteless, odorless gas which we may call oxid of carbon. The more common names applied to it are carbonic acid gas and carbon dioxid, the latter being the preferable term. Test for Carbon Dioxid. — In spite of the fact that carbon dioxid has no color, taste, or odor, we can easily demonstrate its presence in the following way. If we put some clear limewater1 into a bottle in which carbon dioxid has been formed by burning wood, we find after shaking that the liquid loses its transparency and becomes milky. This change in limewater is always caused by carbon dioxid and by nothing else. Mineral Substances. — In our experiments thus far we have watched the formation of water (oxid of hydrogen) and the oxids of phosphorus, sulphur, and carbon. Our match is at last reduced to ashes. These we know will not burn. We may heat them to a red or even white heat, but in most cases they remain wholly unchanged, and on cooling resume their gray or white appearance. The ashes of the wood are the mineral matters that were obtained from the earth by the living plant. Definitions. — If we keep in mind the experiments we have described, certain important definitions will now become clear to us. All the materials of which the universe is composed may be divided into two classes, namely, chemical elements and chemical compounds. Elements. — Of the materials of the universe there are certain substances which chemists are unable to make any simpler in their composition. Hence they are called chemi- cal elements. Over seventy of these elements are known, some of the most common being the carbon, oxygen, and sulphur that we have been studying. The names of these 1 Limewater is made by dissolving ordinary quicklime in water. The solution, after it is strained or filtered through porous paper, is as clear as ordinary water. LESSONS IN CHEMISTKY 9 elements are constantly used in science, and it has been found convenient to refer to these substances by symbols, the first letter or letters of the name being used in most cases. Thus we mean carbon when we use the capital letter C; 0 stands for oxygen; S for sulphur; and P for phosphorus. I stands for iodine, and so Ee (Latin ferrum = iron) is used for iron. An element may be defined as a sub- stance that cannot be decomposed into simpler substances. Compounds. — We have seen that a certain amount of heat causes the element phosphorus to unite with some of the element oxygen, and that thus a new substance is formed called oxid of phosphorus ; more heat will produce oxid of sulphur by a chemical union between sulphur and oxygen, while at a still higher temperature carbon unites with oxygen, forming oxid of carbon or carbon dioxid. All of these oxids are chemical compounds. Hence a chemical com- pound may be defined as a substance that can be decomposed into simpler substances. A compound, therefore, is formed by the chemical union of two or more elements. We will now consider the composition of two of the most important of the compounds that we have been studying. Eepeated experiments have proved that one part of carbon combines with two parts of oxygen. Chemists, therefore, give to the gas thus formed the name carbon dioxid and represent its composition in the symbol C02 ; both name and symbol tell us that it is composed of one part carbon and two parts oxygen. Water, too, is a compound, a fact that can be proved in the following way. If an electric current is passed through a dish of water, the liquid becomes separated into two gases, one of which is oxygen, and the other a gas called hy'dro-gen (Greek, hu'dor= water + gen = maker). We find, on collecting the two gases, that we get twice as great a volume of hydrogen as of oxygen. Hence we represent the composition of 'water by the symbol H20, which means that two parts of hydrogen are combined with one part of oxygen. That such a combination really takes place can be demon- 10 STUDIES IN PHYSIOLOGY strated by holding a dry tumbler over a flame of burning hydrogen.1 The gas combines with oxygen, and drops of moisture collect on the inside, as we noticed when the match wood was burned. Water, therefore, may be called an oxid of hydrogen. Oxidation. — Since oxygen is always necessary for the ordinary processes of burning, to this chemical action is given the general name, ox-i-da'tion. It may take place slowly, as is the case when we rub a match tip over our fingers,2 or rapidly, as when we scratch a match on sand- paper. In any case oxidation means the chemical union of oxygen with some other substance. It is always accompanied by a certain amount of heat, and often, as in the burning of a match or a candle, by light. Air, as we shall soon learn (p. 13), is not a chemical com- pound, but a mixture of two gases ; for these gases do not form a chemical union. Most of the facts in the preceding paragraphs may be summarized in the following outline : — THE BURNING OF A MATCH Materials in a Match + Oxygen in Air 1. Phosphorus on the tip -f Oxygen (yellow, waxy, solid) 2. Sulphur on the tip (yellow powder) + Oxygen = + Oxygen = 3. Hydrogen in wood (colorless, odorless, tasteless gas) 4. Carbon in wood -f- Oxygen (black, brittle, solid) 5. Mineral matter in wood (white or gray powder) = Compounds Formed Oxid of phosphorus (white fumes of peculiar odor) Oxid of sulphur (invisible gas of suffocat- ing odor) Oxid of hydrogen (water) (colorless, odorless, taste- less liquid) Oxid of carbon (carbon di- oxid) (colorless, odor- less, tasteless gas) Ash left after burning (white or gray powder) 1 See " Laboratory Exercises," No. 5. 2 Rusting of iron is a good example of slow oxidation. LESSONS IN CHEMISTRY 11 2. A STUDY OF AIR Preparation of Oxygen.1 — In the preceding study of match- burning, frequent reference has been made to oxygen as one of the elements found in the air. To study the peculiar properties of this gas, we must obtain it in a free state; we can readily get it in this form from compounds that con- tain a large amount of oxygen. One of these is the ordi- nary chlorate of potassium. FIG. 1. — Preparation of Oxygen. We first mix some of the white crystals of this chlorate of potassium with about one third this amount of a black powder called oxid of manganese. Then we put the two into a test tube and close its opening with a stopper through which is passed a bent glass delivery tube (see Fig. 1). The other end of the latter dips beneath the water in a collect- ing tray. When heat is applied to the test tube, the white crystals and black powder are made to give up some of the oxygen which they contain. The gas passes through the delivery tube; and since it does not readily dissolve in water, it comes off in bubbles and escapes into the air. Atmospheric Pressure.2 — Suppose now we fill a wide- mouthed bottle with water, cover the top with a square of glass (Fig. 1), and invert it in the tray of water, removing 1 See "Laboratory Exercises," No. 2. 2 See " Laboratory Exercises," No. 4. 12 STUDIES IN PHYSIOLOGY the glass plate from the month of the bottle when it is just over the end of the delivery tube. The bottle still remains filled with water. We have learned (p. 6) that the atmos- phere above the earth is about fifty miles in thickness. On every square inch of the earth's surface at the level of the sea this air presses down with a weight equal to about fifteen pounds. Hence if our tray happens to measure seven by ten inches (seventy square inches), the atmospheric pressure on the surface of the water will be seventy times fifteen pounds, or ten hundred and fifty pounds, which is over half a ton. It is this downward pressure of the air on the surface of the water that keeps the bottle filled, since the glass bottom of the bottle prevents a like downward pressure on the water within. Collection of Oxygen. — If now we continue to heat the mixture of chlorate of potassium and oxid of manganese, the bubbles of oxygen will rise into the bottle and gradually displace the water. When the bottle is filled with the gas, we close it with the glass plate, and turn it right side up. After we have filled several bottles in the same way, we are ready to determine some of the characteristics of this most important element. Physical Properties of Oxygen. — % physical properties we mean those characteristics of a substance that can be determined by the senses. If the experiment described above has been carried on slowly, and if the gas is passed through bottles of water and caustic soda, the oxygen is seen to be colorless; when we lift the cover and smell of the gas, it is found to be odorless ; and by inhaling some into our mouth we learn that it is tasteless. We might of course expect these results, since fresh air, in which oxygen is present, is likewise colorless, tasteless, and odorless. Chemical Properties of Oxygen. — The striking chemical property of oxygen is shown by the following experiments. Let us set fire to a piece of wood and then extinguish the flame, leaving a glowing spark at the end. Carefully removing the glass plate from one of the bottles of oxygen, LESSONS IN CHEMISTRY IB we thrust in the glowing stick. It immediately bursts into flame and burns brightly until all the oxygen is used. Brilliant fireworks can be made by burning phosphorus or sulphur in the other bottles we filled. Even a steel watch- spring, or piece of picture wire, if the tip is dipped in burn- ing sulphur, catches fire in pure oxygen and throws oft' flashing sparks of burning metal. We see, then, that the most important chemical property of oxygen is its power to make things burn. When any combustible substance is heated sufficiently, the elements of which it is composed unite with the oxygen, and thus are formed the compounds we have called oxids. Preparation of Nitrogen.1 — The other gas found in air is called ni'tro-gen. These two elements, oxygen and nitrogen, are not chemically united ; they are simply mixed, as we might mingle sand and sugar. We can easily take the sugar from the sand by putting the mixture in water ; the sugar is dis- FlG 2 _ reparation of Nitrogen, solved, while the sand re- mains untouched. Chemists can also remove the oxygen from a certain quantity of air, leaving free nitrogen. The materials required for the experiment are a tray of water, a wide-mouthed bottle, a bit of phosphorus the size of a pea, and a piece of cork large enough to float the phos- phorus on the water. Placing the phosphorus on the cork and lighting it, we quickly cover it with the mouth of the bottle in such a way that the rim reaches just beneath the surface of the water. The phosphorus burns readily for a time, and the bottle is soon filled with the white fumes of oxid of phosphorus. When all the oxygen has been used, the flame dies out. As we watch the experiment, the white fumes are seen to be gradually settling toward the surface 1 See "Laboratory Exercises," No. 3. 14 STUDIES IN PHYSIOLOGY of the water ; at length they disappear altogether. Mean- while the water has been slowly rising into the bottle. When this upward movement has ceased, we cover with a glass plate the mouth of the bottle and quickly turn it right side up, thus keeping within the bottle the water that arose from the tray. A Test for Acids.1 — Let us first examine the water we have collected in the bottle. If we drop into ordinary water a bit of paper treated with a kind of vegetable stain called blue litmus, the color remains unchanged ; but if we dip the blue paper into any kind of acid substance, as lemon juice, or vinegar, the color becomes red. The presence of acids, then, may be readily demonstrated by using blue litmus. When we test in this way the water we obtained in the pre- ceding experiment, we find it is acid. The white fumes of oxid of phosphorus, which we saw settling upon the surface of the water, have been dissolved and have made the water acid in its properties. The Composition of Air. — While the phosphorus was burn- ing, it continually took away oxygen from the air confined in the bottle until all the oxygen was used. Hence, after the oxid of phosphorus thus formed had been dissolved in water, a space was left. But the pressure of the atmosphere on the surface of the water outside the jar caused the water to rise and fill this space as fast as the oxygen was with- drawn. The water, therefore, comes to occupy the space in the bottle which, at the beginning of the experiment was taken up by oxygen. If we measure the capacity of the bottle and then measure the amount* of water, we see that the latter takes up about one fifth of the space in the bottle. This means that air is composed of about one fifth oxygen and four fifths nitrogen (see Fig. 3). (Much more accurate results can be obtained if a piece of phosphorus is floated on the cork and allowed to oxidize slowly within the bottle of air for two or three days.) 1 See "Laboratory Exercises," No. 7. LESSONS IN CHEMISTRY 15 Properties of Nitrogen. — On applying to nitrogen the same tests that we used in studying oxygen, we find the physical properties of the two gases are very similar. Both are colorless, tasteless, and odorless gases. In chemical properties, however, they differ widely. When we thrust into a jar of nitrogen a glowing splinter of carbon, the spark is at once extinguished. Burning sulphur is affected in the same way, and even phosphorus ceases to burn as soon as it comes in contact with nitrogen. All this means that phos- phorus, sulphur, and carbon will not combine with nitrogen as they do with oxygen. In fact, nitrogen may be character- ized as the least active of all elements. It does not readily unite with any other element, and the compounds in which nitrogen is found are very unstable. Gunpowder and nitro- glycerin owe their explosive power to the fact that the nitrogen present easily loses its hold upon the other ingredi- ents. The nitrogen in the air prevents oxidation from going on at too rapid a rate. COMPOSITION OF THE AIR PROPORTION -OF INGREDIENTS PHYSICAL PROPERTIES OF INGREDIENTS COLORLESS, ODORLESS, TASTELESS GAS. COLORLESS, ODORLESS, TASTELESS GAS. CHEMICAL PROPERTIES OF INGREDIENTS WILL NOT BURN WILL NOT MAKE THINGS BURN, USED TO DILUTE THE OXYGEN. WILL NOT BURN MAKES THINGS BURN BY COMBIN- ING WITH THEM TO FORM OXID8. FIG. 3. — Composition of the Air. 16 STUDIES IN PHYSIOLOGY 3. THE CHEMICAL COMPOSITION OF THE HUMAN BODY We are now to consider the application of some of these principles of chemistry to the study of the human body. Chemists have accurately determined the chemical composi- tion of the various parts of the body, and we will discuss some of the most important substances that have been shown by analysis to be present. Water. — The great importance of water in the composi- tion of living substance is evident from the fact that it 'forms about 62% of the weight of an adult man. Hence, if all the water were removed from the body of a man weighing one hundred and sixty-five pounds, the solids that remained would weigh but a little over sixty pounds. The different organs vary greatly in their percentage of water : bones con- tain about 22%, muscles have 75%, and the kidneys 82 %. Mineral Matters. — Mineral matters are found in greatest quantity in the bones. When we burn bones, about one third of the weight disappears, the remaining two thirds being bone ash, which is the mineral matter. Every part of the body, however, contains some mineral ingredients, for when muscle, liver, brain, or blood is burned, in each case there remain some traces of ash. Gases. — A large amount of the gas oxygen is taken into the lungs, whence it is distributed to all the organs by the blood. We shall find that in our bodies, as well as in the experiments with the match this oxygen performs the all-important function of causing oxidation. One of the products of this oxidation is the gas we have already con- sidered ; namely, carbon dioxid. If we blow through a tube or a straw into a glass of clear limewater, the liquid be- comes milky. Our breath is therefore constantly removing from our bodies a gas exactly like one of those formed by burning the match. Fats. — The amount of fat in the body varies greatly in LESSONS IN CHEMISTRY 17 different individuals, but it is always present in some quan- tity. Muscle, however lean, contains particles of fat; fat constitutes a small percentage of the blood; it fills the spaces in the interior of bones ; and it is often deposited in considerable quantity in the deeper layers of the skin. When fat is heated, it first melts to a liquid. At a higher temperature it will scorch, and the black residue shows the presence of carbon. In the body this fat is burned by com- bining with oxygen, and this is one of the ways in which we are kept warm. If we were to eat nothing for several days, we could still be kept warm and be able to do a certain amount of work, a result due largely to the slow oxidation of the fat stored in various parts of the body. Carbohydrates. — The substances we know as starches and sugars are made up of the three chemical elements, carbon, hydrogen, and oxygen, and the hydrogen and oxygen of these compounds are always in the same proportion in which they occur in water (that is, H20). Hence these compounds are called car-bo-hy' drates (carbon +hy dor = water). In the blood and other animal tissues we find some of the carbohydrate called grape sugar.1 Another carbohydrate, known as animal starch or glycogen, is found In the liver.2 Carbohydrates, like fats, contain a large amount of carbon, which also unites with oxygen. A sec- ond ingredient of both of these classes of compounds is hydrogen ; it readily combines with oxygen to form water. The fats and carbohydrates found in the composition of the body may be regarded as stored-up fuel which can be drawn upon in case of need. Like the engine, we are kept warm and enabled to do work by the oxidation of fuel. 1 The chemical composition of grape sugar is represented by the chemical formula C6Hi206, which means that every molecule of grape sugar contains six atoms of carbon, twelve atoms of hydrogen, and six atoms of oxygen. 2 Glycogen is comp6sed of six atoms of carbon, ten atoms of hydro- gen, and five atoms of oxygen, its chemical formula being C6H1005. c 18 STUDIES IN PHYSIOLOGY Nitrogenous Substances. — The most important substances in the living body are the ni-trog'e-nous compounds. They are all characterized, as the name implies, by the presence of the element nitrogen (symbol N). Some of these com- pounds which are present in all living substance are known as pro'te-ids or albuminous substances. Without exception, proteids consist chiefly of the elements carbon, hydrogen, oxygen, nitrogen, and sulphur, and often other elements are present in their composition. They are the most complex substances in the body.1 From the carbon of the proteids also there is formed by oxidation the waste gas carbon dioxid, which, as we have demonstrated, is thrown off from the lungs. Another im- portant waste compound that comes from the oxidation of proteids is a substance known as u're-a. Urea contains most of the nitrogen that cannot be further used by the body. It is taken from the blood by the kidneys and forms the principal solid constituent dissolved in the urine. The summary on the following page contains in brief the principal facts we have learned in regard to the chemical composition of the body. 1 The composition, for example, of the proteid hem-o-glo'bin (Greek hai'ma= blood) which gives the red color to the blood, is said by one chemist to be CeooHgeoOngN^SsFe (Fe being the symbol for iron). This formula means that a molecule of the compound hemoglobin consists of over eighteen hundred atoms, six hundred of which are carbon, nine hundred and sixty, hydrogen, etc. LESSONS IN CHEMISTRY 19 THE CHEMICAL COMPOSITION OF THE HUMAN BODY SUBSTANCES FOUND FORM OF SUB- STANCE COMPOSED OF WHERE FOUND IN THE BODY A. Compounds found in the body. 1. Water. Liquid. H and O In all parts of the (=H«0). body. 2. Mineral Solid or in so- Salts of po- Principally in bones ; matters. lution. tassium, cal- found also in other cium, etc. parts. 3. Fats. Solid or in so- C, H, and O. In muscles, bones, lution. blood, and beneath the skin. 4. Carbohy- Solid or in so- C, H, and 0 Principally in liver, drates. lution. (H and O in blood, and muscles. proportion of H20). 5. Proteids. Solid or semi- C, H, 0, N, In all living sub- fluid. S, etc. stance. B. Element causing the oxidation of the body. 6. Oxygen. Gas. 0. Supplied from lungs by blood to all parts of body. C. Products of oxidation of the body (= waste substances). 7. Water. Gas or liquid. HandO Thrown off from body (=H20). by lungs, skin, kid- neys. 8. Carbon Gas. C andO Taken by blood from dioxid. (=COa). all parts of body to lungs and skin, whence it is given off. 9. Urea. Solid (in so- C, H, O, and Taken by blood from lution) . N. all parts of body to kidneys and skin, whence it is given off. CHAPTER III A STUDY OF LIVING SUBSTANCE 1. THE GENERAL STRUCTURE OF ANIMAL BODIES Vertebrates and Invertebrates. — All animals may be divided into two great classes, known respectively as the ver'te-brates and the in-ver'te-brates. To the first group belong the animals that have a backbone. We are all familiar with common vertebrates like fishes, frogs, snakes, birds, and cats. Insects, worms, and clams, on the other hand, have no backbone; hence they are called invertebrates (i.e. animals without vertebrse). Regions of the Body. — In man and in most other verte- brates we can distinguish the head and neck region, the trunk, and the four ap-pend'ag-es or limbs which are at- tached to the trunk, namely, two arms and two legs, or, as they are more often called in descriptions of the lower ani- mals, the four legs. Since frequent reference will be made in the following pages to different vertebrates and inverte- brates, we must become familiar at the outset with certain terms that will locate definitely corresponding regions in all animals. Man walks on two appendages (the legs) ; the long axis of his trunk is vertical ; and above his body is his head. But dogs and other four-footed animals have a horizontal trunk with the head attached in front. Hence the same adjective cannot be used to describe the position of the head of man and of quadrupeds. Biologists have, therefore, adopted the term an-te'ri-or (Latin an'te = before) which can be applied 20 A STUDY OF LIVING SUBSTANCE 21 to the head end of any animal. A corresponding term pos- te'ri-or (Latin post = after) refers to the opposite end of the body. We can include, for instance, under the term anterior appendages the wings of a bird, the front feet of a horse, and the arms of man, since all these appendages are located toward the head end of the trunk. The descriptive term dor'sal (Latin dor1 sum = back), when applied to vertebrates, 'always designates the region of the body in which the backbone is found. If this term is used in describing the structure of invertebrates, it refers to the upper surface of the animal. Ven'tral (Latin ven'ter = belly), on the other hand, designates the under or, in man, the front surface. Both in man and in the horse the mouth opening is on the ventral surface of the body, even though its position apparently differs so much in the two animals. Organs.1 — When we study the body more closely, espe- cially its interior, we find, in various regions, parts that carry on special kinds of work. Within the chest cavity in the upper or anterior part of the trunk is the heart, which forces the blood through the body. Here, also, are the lungs, which take in oxygen and give it to the blood, and which remove some of the waste matters from the body. Below the heart and lungs, or in other words, posterior to the trans- verse muscular partition, called the di'a-phragm, are the stomach and the intestines, the liver and the pancreas, all of which help to change our food into liquid form. Here, too, are the kidneys and the spleen. All these and other parts of the body, like the brain, the spinal cord, and the hands, are called organs. An organ is a part of a liv- ing body that has some special work to do : this special work is called its function. Our hands are organs, because with 1 On the next page is a* figure of the internal organs of a rabbit (Fig. 4). In this figure most of the organs enumerated above can be identified ; the form and position of these organs in the human body, however, are somewhat different, as one sees after studying the figures on pp. 76, 99, 130, and 255. 22 STUDIES IN PHYSIOLOGY FIG. 4. — The Internal Organs of a Rabbit. A = cavity of the chest. , a = cut ends of ribs. B = diaphragm. (7 = ventricles of heart. D = auricles of heart. E =i artery to lungs. F = aorta (artery to rest of body) . G = lungs, collapsed. JI=part of covering of lungs (pleura). /= lower end of breast bone. K = portion of body wall between chest and abdomen. L — liver, lying toward left of body. M= stomach. N, O = small intestine. P = coecum (part of intestine). Q = large intestine. A STUDY OF LIVING SUBSTANCE 23 them we take hold of things and make the definite move- ments required in writing, drawing, and sewing. Tissues. — When we pinch the arm and the hand, we feel the hard bones that form their skeleton. We can raise from the bones the softer fleshy material called muscle. By straightening back our fingers as far as possible, we can see and feel on the back of the hand the tough cords or tendons of connective tissue. Run a clean needle point into the finger ; blood flows and we feel pain. In this way we discover two more of the materials of which our hand is composed, name- ly, blood and nerves. All these parts of the body we have enumerated are known as tissues. For the present, a tissue may be defined as one of the building materials of which an organ is composed (see p. 28). * In the hand we have evidence of the presence of bone tissue, muscle tissue, connective tissue, blood tissue, and nerve tissue. Other kinds of tissue will be discussed in the pages that follow. 2. CELLS, THE UNITS OF LIVING SUBSTANCE When we have considered the characteristics of the tissues, we can go no further in our study of structure without the aid of the compound microscope. With this instrument we dis- cover that the tissues are by no means the simplest parts of an animal. In order to get a clear idea of the units of which living substance is composed, let us turn for a time from the study of the human organism and consider some of the lowest of animal forms. The Amoeba. — The material for our work is best obtained by securing some of the mud and decaying leaves from the bottom of a pool of water. When we come to examine a drop of this sediment with microscope lenses that magnify two or three hundred times, a wonderful scene of life is revealed. Our attention is fixed upon a multitude of minute 1 It is important to bear in mind that a tissue is not necessarily or usually a thin membrane like tissue paper ; bony tissue, for instance, has considerable thickness and great strength. 24 STUDIES IN PHYSIOLOGY living forms that hurry across the field of our vision with bustling activity. Here and there are little creatures that move more slowly, often by performing a "series of somer- saults. If we examine the drop very closely, rod-shaped organisms of exceeding minuteness (bacteria, see p. 32) be- come visible, which are bumping against one another in their tremulous activity. The special object of our search in this whirlpool of life is a microscopic animal about one one-hundreth of an inch in diameter, called the a-mce'ba. This minute creature is a droplet of colorless, semi-fluid sub- stance, at first perhaps more or less spherical in form. But as we look at our specimen, we notice that its shape is chang- ing. On one side some of the material of which FIG. 5. - An' amoeba, highly magnified. the amoeba is composed c.vac = contractile vacuole (probably for IS slowly streaming out excretion). to form a bulging pro- £ = SS2f£t (pooped.) Action or process. This extension is called a, false foot, which may increase in size until all of the substance of the animal has passed into it. By pushing out these processes in front and pulling up its body matter from behind, the amoeba moves slowly from one part of the slide to another. This characteristic method of locomotion is known as amoeboid. If we suddenly jar the slide, all the semi-fluid substance, in the extended false feet is drawn back toward the center of the animal, and the amoeba again assumes its spherical form. Structure of a Cell. — The amoeba is one of the simplest of living creatures. It is known as a one-celled animal. A STUDY OF LIVING SUBSTANCE 25 We must now try to get a clear idea of what is meant by the term cell, since a "knowledge of cell structure and cell activity is absolutely essential for a clear understanding of biology. If the amoeba is colored with certain stains, we can see a darker spot in the center to which is given the name cell nu'cle-us (Latin nucleus — a small nut). The rest of the animal is called its cell body. The living sub- stance of which nucleus and cell body are composed is now universally known as pro'to-plasm. A cell, therefore, in the biological sense is a bit of protoplasm containing a nucleus.1 Cells of the Blood.— Keeping in mind the facts we have learned in our study of the amoeba, we will now return to the structure of the hu- man body. Let us first examine with the micro- scope a drop of fresh blood.2 We soon find it is not the simple red liquid it seems to be; it consists of solid par- ticles, called blood cor'pus-cles, floating in a watery liquid 1 The term cell was first used in describing the structure of plants, because in plant tissues the protoplasm is inclosed in little boxes or rooms, the boundaries of which are called cell walls. The botanists who first used the term cell noticed the walls before protoplasm was discovered. The cell walls of plants are formed of cel'lu-lose, a substance resembling starch. Many animal cells do not have a cell wall. 2 The blood can be easily obtained by tying a cord tightly about the finger and then pricking it with a clean needle. A drop is squeezed out upon a glass slide and covered with a thin cover glass. FIG. 6. — Blood Corpuscles. a, 6 = white corpuscles (nucleus not seen). c, d, e — white corpuscles (nucleus seen). r = red corpuscles (surface view) . r' — red corpuscles (edge view) run together in piles. 26 STUDIES IN PHYSIOLOGY known as blood plasma. Like the amoeba, these corpuscles are single cells. Two kinds may be distinguished, which from their color are known as red and white corpuscles. There are three hundred to seven hundred times as many red corpuscles as white. But we shall consider the white corpuscles first because of their similarity to the amoeba both in structure and in activity. Each corpuscle consists of a minute bit of protoplasm in which is imbedded a nucleus. These blood cells have also the characteristic amoeboid movement. By this method of locomotion they can creep along in a direction opposite to that of the blood current, and they have even been seen forcing their way through the walls of small blood vessels by pushing out false feet. They then wander about in the tissues of the body and do us great service, as we shall see, especially in time of disease. The red corpuscles have no power of independent motion. They are circular disks, concave on both surfaces.1 Some idea of the minute size of these cells may be gained from the fact that five millions of them are floating about in a drop of blood the size of a pin head. There is no nucleus in the red corpuscles; yet we consider them as modified animal cells, since they are formed from cells having a nucleus. Cells in Other Tissues. — If we examine microscopically nerve tissue, muscle tissue, or any other building material of animal bodies, we find each and all of them to be composed of cells. These vary somewhat in size, although all are microscopic. As we shall see there are characteristic forms of cells for each tissue ; but every animal cell, so far as we know, has a cell body and a nucleus. Intercellular Substance. — When we look at the end of a fresh soup bone, we see a white shining tissue, known as 1 A good model of a red corpuscle can be made from clay or putty. Roll a small mass about the size of the finger tip into a sphere, flatten it until the thickness is one fifth the diameter ; then pinch the flattened disk between the thumb and. finger. A STUDY OF LIVING SUBSTANCE car'-ti-lage or gristle. Placing a thin section of this cartilage beneath the micro- scope, we can dis- .-:,>. }n tinguish cells looking somewhat like blood corpuscles. The nu- cleus and body of each cell become visible when the tissue is stained ; but instead of floating in a liquid, as did the red corpus- cles of the blood, these cells are imbedded in solid cartilage. The term in'ter-cel'lu-lar substance (Latin, in'ter = between + cel'lu-la = cell) is applied to this tough gristle which is a product of the cartilage cells. Another kind of intercellular substance is found in bone tissue. If a thin section bone is ;> FIG. 7. — Thin Section of Cartilage, highly magnified. a = group of two cartilage cells. b = group of four cartilage cells, c = cell body of cartilage cell. m = intercellular substance (cartilage). n = cell nucleus of cartilage cell. with scope, a of dried examined the micro- tiny spaces are seen, which, when the bone was alive, were filled with the proto- plasm of cells. These bone cells are usually more or less oval in out- line, but the proto- plasm of each cell body extends outward in many fine irregu- lar processes that approach closely to the processes from FIG. 8. —Thin Section of Bone, magnified 110 times. Photographed through the microscope. Black irregular spots are filled with the bone cells. White spaces between are formed by bony intercellular substance. 28 STUDIES IN PHYSIOLOGY other cells. A bone section, therefore, looks as though it were filled with a multitude of amcebas, each of which has extended several branching false feet. Between these irregular bone cells is the hard intercellular substance that gives rigidity to this kind of tissue. Definition of a Tissue. — A tissue may now be defined as a building material of an organ, composed of cells of the same kind, together with more or less intercellular substance. 3. SOME OF THE PROPERTIES OF PROTOPLASM Microscopic Appearance. — Protoplasm, when examined with the highest powers of the micro- scope, appears as a colorless, semi- fluid substance, in which are usually seen solid particles or granules. The nucleus is commonly found near the center of the cell and is composed of protoplasm denser than that of the cell body. The appearance and consistency of the protoplasm surrounding the nu- cleus, that is in the cell body, may be well represented by the raw white of an egg ; but in making this comparison one should bear in mind that the white of egg is not living substance. Chemical Composition. — Living substance contains a large amount of water, which keeps it semi-fluid. If we dry pro- toplasm, we kill it. While the amount of water in the different tissues, as we have seen, varies considerably, it con- stitutes on the average nearly two thirds of the body weight. The most important constituents of living cells, however, are the proteids. These complex substances are always present in protoplasm, and, so far as we know, they can be made only by protoplasm. Particles of sugar, fat, and other food sub- stances, are usually found in protoplasm and help give to the cell body its granular appearance. FIG. 9.— Parts of a Cell. p = protoplasm of cell body. n = nucleus. A STUDY OF LIVING SUBSTANCE 29 Production of Energy. — Between a working locomotive and our bodies, as already noted, there are many points of re- semblance. The building materials of an engine are brass, wood, glass, and iron ; these may be regarded as the tissues of the machine. A combination of several of these materials form the boiler, the wheels, the whistle, and the headlight ; and since each of these parts of the engine has some special work to do, we may call them organs. Again, like our bodies, the engine must be continually supplied with water and fuel in order to do its work. As coal is burned in the locomotive to give heat and power, so food is oxidized in animals ; and in both kinds of machines waste materials are formed and thrown off. Growth. — But the comparison between our bodies and a locomotive must not be carried too far. In the first place, no one ever knew of an engine to begin its existence as a small machine and then to increase in size little by little until its weight had multiplied twenty times. Yet this is true of the human body. An average child at birth weighs about seven pounds ; the weight of a grown man commonly exceeds one hundred and forty pounds. None of the coal and water put into the engine is changed into the brass, iron, or other " tissue " of the machine. But in the human body a great part of the food we eat becomes muscle, bone, and brain, for these animal tissues in some unknown way can make over lifeless food materials into living substance. One of the most striking properties of protoplasm is this power to make more protoplasm, or in other words, to grow. To this process is given the name as-sim-i-la'tion (Latin ad = to + similis = like) ; for when muscle tissue, for example, takes from the blood its supply of food, the latter is made by the muscle into protoplasm like to itself. Repair — By continual use parts of the locomotive become worn or broken, and the engine must go to the machine shop for repairs. In our bodies, too, the tissues are being con- stantly worn away. Every time we use our muscles some of 30 STUDIES IN PHYSIOLOGY the protoplasm is oxidized ; every time we think or exert our will power, some of the living tissue of the brain is probably changed into dead waste material. But, in contrast to lifeless machines, our bodies are self-repairing. The food we eat not only goes to increase the size of the body ; it also furnishes material to make good the wear and tear of every- day life. In the human body, then, a given kind of food substance may at one time be used for the growth of the body ; at another time it may serve for the repair of the tissues; or still again, as in the engine, it may be burned to keep us warm and to give us power to work. The processes of growth, repair, and the production of energy in the human body are un- doubtedly extremely complex. • Oxidation is probably only one of the processes involved. To the whole series of changes by which food is transformed into protoplasm or is made to yield energy is given the name me-tab'o-lism (Greek metabole = a change). Cell Division — Since cells are the units of which the body is composed, it is evident that when the tissues grow, cells must increase either in size or in number. Biologists know that cells remain nearly constant in size, however large the body may grow. The number of cells, however, increases enormously as one grows from childhood to adult life. The formation of new cells can be watched in animals like the amoeba. Some little time before division is to take place the cell ceases to move about, pulls in its false feet, and be- comes more or less spherical in form. Important changes appear first in the nucleus. It gradually assumes the form of a dumb-bell ; the knobs at the end of the dumb-bell then draw away from each other, until finally the connection is broken between the two halves of the nucleus. The amoeba has now two nuclei, one at each end of the cell. Meanwhile the cell body has been assuming a more or less oval form, and its protoplasm begins to divide into halves. At A STUDY OF LIVING SUBSTANCE 31 the end of the process the " mother cell " has been equally divided into two " daughter cells," each having a nucleus and cell body. The daughter cells now move about, take in food, grow, and in turn divide. The amoeba " family " now consists of four " granddaughter cells.'7 The process of cell division in many of the human tis- FIG. 10. — An Amoeba in Successive Stages of Division. The dark spot is the nucleus. The light spot is the contractile vacuole. sues is far more complicated than in the amoeba. The essential facts are true, however, in almost every case of cell division. They are these : (1) the material of the mother nucleus is divided in such a way that each daughter cell receives exactly one half; (2) a more or less equal division of the material of tne cell body follows j (3) this 32 STUDIES IN PHYSIOLOGY process is followed by a period of assimilation in which both daughter cells increase in size. Before we leave this discussion of living substance, it will be well to consider the single-celled organisms known as bac-te'ri-a or germs, since they have most important rela- tions to the health of our bodies. Yeast, too, will be dis- cussed, because of its interesting physiology and because of its importance in connection with bread- and liquor-making. 4. A STUDY OF BACTERIA 1 Changes caused by Bacteria. — If milk is allowed to stand in a warm room, it becomes sour to the taste, and it thickens or curdles. Meat that has been kept for a considerable time de- cays, giving off disagree- able odors. We know, too, that water in which flower stems have been kept, at length becomes putrid. All these, and countless other changes, are caused by bacteria, those microscopic organ- isms that were hardly dreamed of forty years ago. Microscopic Appear- ance of Bacteria. — The thin scum formed on FIG. which 11. — Rod-shaped Bacteria cause Lock-jaw. Magnified about 800 times. Photographed through the microscope. Some of the bacteria have an oval light colored spore near one end. scum the top of all stagnant water consists of millions of bacteria. When we examine with the highest powers of the microscope a bit of this scum, these micro-organisms are seen to have several differ- 1 See "Laboratory Exercises," No. 49. A STUDY OF LIVING SUBSTANCE 33 ent forms. Some are rod-shaped (like a firecracker), some are spherical, others are egg-shaped, or spiral-shaped like a corkscrew. Each bacterium is a tiny bit of translucent protoplasm, inclosed in a cell wall of cellulose. Thus 'far no nucleus has been discovered in any kind of bacteria. Be- cause of their cellulose walls, and because of their likeness to certain low forms of green plants, biologists now regard these organisms as plants rather than animals. Some of the rod-shaped bacteria have one or more long hairlike projections from the ends, called cil'-i-a, which give the germs still further resemblance to firecrackers. These cilia lash about furiously, and thus drive the cells through the water. The spiral bacteria roll over and over, and ad- vance in a spiral path like a corkscrew or spiral spring. Other forms have rapid movements, but it is not known how they are accomplished. Size of Bacteria. — It is very difficult to get any clear notion of the extreme minuteness of bacteria. It means but little to say that the rod-shaped forms are one five-thou- sandth of an inch in length. The imagination may be somewhat assisted if we remember that fifteen hundred of them arranged in a procession end to end would scarcely reach across the head of a pin. Reproduction of Bacteria. — When conditions are favor- able, the production of new cells goes on with marvelous rapidity. The process is something as follows. The tiny cells take in through the cell wall some of the food materials that are about them, change this food into protoplasm, and thus increase somewhat in size. The limit is soon reached, however, and the bacterium begins to divide crosswise into halves. The mother cell thus forms two daughter cells by making a cross partition (cell wall of cellulose) between the two parts. If the daughter cells cling together, a chain or a mass is formed. Oftentimes they separate entirely from each other. In either case the whole mass of bacteria is called a colony. 34 STUDIES IN PHYSIOLOGY It usually takes about an hour for the division to take place. Suppose, then, we start at 10 o'clock some morning with a single healthy bacterium. If conditions are favor- able, there would be two cells at 11 o'clock, and by 12 o'clock each of these two daughter cells would form two granddaughter cells ; the colony would then number four individuals. Should this process continue for 24 hours or until 10 o'clock on the day after the single bacterium began its race, the colony would number 16,776,216 bacteria. " It has been calculated by an eminent biologist," says Dr. Prud- den,1 " that if the proper conditions could be maintained, a rodlike bacterium, which would measure about a thousandth of an inch in length, multiplying in this way, would in less than five days make a mass which would completely fill as much space as is occupied by all the oceans on the earth's surface, supposing them to have an average depth of one mile." Necessary Conditions for the Growth of Bacteria. — Such start- ling possibilities as those suggested in the preceding section fortunately can never become realities, for the favorable conditions to which we have referred soon cease to exist. Bacteria, like all other living organisms, require food, oxy- gen, moisture, and a certain degree of warmth. Let any one of these conditions be withheld, and the cells either die or cease to be active. Sometimes, when food or moisture begins to fail, the protoplasm within each cell rolls itself into a ball and covers itself with a much thickened wall. This protects it until it again meets with conditions favor- able for growth. The process we have been describing is known as spore formation; the tiny protoplasmic sphere is called a spore, and its dense covering a spore wall. In this condition bacteria may be blown hither and yon as a part of the dust. They may be heated even above the temperature of boiling water without being killed. When at length they 1 " The Story of the Bacteria," by Dr. T. Mitchell Prudden. G. P, Putnam's Sons, N. Y. A STUDY OF LIVING SUBSTANCE 35 settle down on a moist surface that will supply them with food, the spores burst their thick envelope, assume once more their rod-shaped or spiral form, and go on feeding, assimilating, and reproducing their kind. Many forms of bacteria feed upon dead animals and plants, cause them to decay, and thus finally convert them into carbon dioxid, water, and other simple compounds that can be used by the higher plants. In this way these micro- organisms are of incalculable benefit to mankind and to all forms of life, for they keep the surface of the earth from becoming a vast cemetery. To the action of bacteria also are due many of the flavors of meats and cheese. Unfortunately, however, there are certain germs that find favorable conditions for growth only in living animal tissue. Thus the bacterium of consumption grows in the lungs, the germ of diphtheria in the throat, and the bacteria that cause typhoid fever in the intestines. These disease-producing germs are called by Dr. Prudden "Man's invisible foes." Yet wonderful progress is being made in the fight against them. We have learned how to check the ravages of chol- era, typhoid, and diphtheria, and even consumption is found to be a preventable disease. Further discussion of bacteria will be found in several of the subsequent chapters. 5. A STUDY OF YEAST AND FERMENTATION1 Changes Caused by Yeast. — A small piece of a cake of com- pressed yeast, mixed in a spoonful of water, forms a milky fluid that is much like so-called bakers' or brewers' yeast. When this is added to a cupful of water, in which a spoon- ful of molasses has been dissolved, one has a convenient mixture with which to carry on experiments in fermentation.2 1 See "Laboratory Exercises," No. 48. 2 This mixture should be placed in a loosely stoppered bottle, for if the bottle is tightly closed, an explosion may be caused by the pressure of the gas that is formed. 36 STUDIES IN PHYSIOLOGY If the yeast mixture is set aside in a warm place (70 to 90 degrees Fahrenheit) for a short time, it begins to " work," and bubbles of gas rise to the surface. At the end of several hours, we notice that the sweetness of the molasses is dis- appearing, that the mixture begins to smell sour, and that a sharp, biting taste is becoming evident. All these changes are caused by the growth of living yeast cells. Now, what is the gas that is formed in this process, and what causes the changes in taste and odor? To answer these questions we must carry our experiments still further. When the mixture is "working" well, the bottle should be tightly closed with a rubber stopper, through which extends one arm of an inverted U-shaped tube. The other end of this tube should run over to the bottom of a test tube half-filled with limewater. The gas that has been rising through the yeast mixture, now passes through the U-tube, and as it comes in contact with the limewater, the latter changes to a milky- white color. This proves, as we have seen on p. 8, that the gas formed during the growth of yeast is carbon dioxid. Distillation. — After " working " a day or two, the yeast mixture will have a strong taste and odor. A part of it should then be poured into a glass Florence flask (commonly used in the chemical laboratory for boiling liquids), and the mouth should be closed by a rubber stopper. The short arm of a long delivery tube should be passed through this stopper. When the flask is heated gently, some of the liquid is changed to a vapor. If the delivery tube is cooled by cov- ering it with cloths wet in cold water, the vapor condenses into a liquid, which comes from the end of the tube in drops. This operation we have been describing is known as dis-til- la'tion. In distilling a liquid, we first convert it into a vapor, and then condense this vapor into a liquid. After collecting a few spoonfuls, the liquid should be slowly distilled a second time. Then we obtain a colorless fluid that has the distinct smell and taste of alcohol. It burns, too, with a pale blue flame. A STUDY OF LIVING SUBSTANCE 37 Fermentation. — And so we learn that yeast, as it grows in the molasses mixture, changes the sweet substances into car- bon dioxid and alcohol, a process that is known as alcoholic fer-men-ta'tion. Microscopic Appearance of Yeast. — While watching the yeast experiments, we see on the bottom of the bottle a dense, white sediment. If we examine with the microscope a bit of this sediment, we find that it consists t>f innumerable bodies of minute size. These are yeast cells. Each cell is more or less egg-shaped, and is composed of colorless proto- plasm inclosed within a wall of cellulose. By the use of special stains, a nucleus becomes visible. (The spherical dots seen in fresh yeast cells are known as " vacuoles " and are filled with a color- less liquid.) Yeast is regarded as one of the lowest forms of plant life. Reproduction of Yeast. — Most of the cells that we are looking at are not separate individuals, but are strung together in little chains. This fact leads us to a discus- sion of the method of reproduction of yeast. When there is a suffi- cient supply of food, moisture, and Oxygen, Magnified about 200 times. Photographed through the microscope. One can see single cells, mother-and-daughter colo- nies, and near the center a mother cell, two daughter cells, and a granddaughter cell. Fia. 12. —Yeast Cells. and when the tempera- ture is favorable, these living plant cells begin to feed and to grow. They soon reach their full size, and then the cell wall is pushed out at the side by the growing protoplasm. In this way a bud is formed. This continues to grow and 38 STUDIES IN PHYSIOLOGY soon becomes a daughter cell, closed off from the mothei cell by a wall of cellulose. Meanwhile, one or more buds may be forming on the outside of the daughter cells. If all these cells cling together, a colony is formed which consists of a mother cell (largest in size), one or more daughter cells, and several tiny granddaughter cells. The individual cells are easily separated from one another. This method of reproduction is known as budding. Spore Formation is a second way in which yeast reproduces itself. When conditions become unfavorable for further growth, the protoplasm within each cell separates into spores (usually four), and since these bodies are well protected by thick spore walls, they may be blown about in the dust of the air. If they happen to settle upon a surface that supplies food and moisture, these spores develop into yeast cells. For this reason, it is very difficult to keep sweet substances from fermenting, unless they are heated to a high tem- perature and then carefully closed from the air. Alcoholic fermentation is always due to the action of yeast. Uses of Yeast. — The action of yeast in bread-making will be discussed in the next chapter. These minute organisms are also of great commercial importance in the manufac- ture of alcohol and of all kinds of liquors. We have learned that yeast cells are found commonly in the air. As different kinds of fruits ripen, they are usually more or less covered with yeast or its spores. When, there- fore, grapes are gathered and their juice is pressed out, the sweet liquid is soon alive with the busy cells, and fer- mentation begins at once. Wines are produced in this way. In the so-called light wines the percentage of alcohol is small (5 to 12%); in heavy wines it is 15 to 25%. Cider is produced by the fermentation of apple juice. In the manufacture of beer and of other malt liquors, bar- ley is commonly used. The grain is soaked and allowed to sprout for a short time, until the starch is changed to grape sugar. The barley kernels are then killed by heat to pre- A STUDY OF LIVING SUBSTANCE 39 vent further changes, and the grain is then known as malt. When this is put into water, the sugar is extracted. Yeast is then added, and the mass ferments. The beer thus formed contains 2 to 5% of alcohol. Distilled Liquors, or spirits, are obtained from wines and other fermented liquors by the process of distillation, the principles of which have already been explained. Brandy is made by distilling wine, whisky is obtained from fer- mented corn and rye, and rum is manufactured from molas- ses. All of these liquors contain a large percentage of alcohol (40 to 50%). Patent Medicines. — In the issue of Nov. 8, 1902, of Ameri- can Medicine are found the percentages of alcohol in eleven of the widely advertised patent medicines. These percent- ages run from 17 + % (in a nerve medicine) to 44 -|- °/0 (in one of the "stomach bitters"). These "bitters" contain ten times the quantity of alcohol found in beer} and are even stronger than whisky and brandy. Hence, the average drug store, where these patent medicines are freely sold, must share with the liquor saloon the heavy responsibility for the prevalence of the drink habit. THE STRUCTURE OF THE LIVING HUMAN BODY 1. Protoplasm is the living substance, composed largely of proteid, water, and mineral matters. These compounds are made up of C, H, 0, N, S, P, and other elements. 2. Cells of the body are to a large extent composed of pro- toplasm, which forms the cell body and nucleus. 3. Tissues of the body are its building materials, composed of cells of the same kind with more or less intercellular substance. 4. Organs of the body are composed of various tissues, which work together to perform some special function. 1 See also "The Use of Temperance Drinks," pp. 344, 345, by Professor H. P. Bowditch, in "Physiological Aspects of the Liquor Problem." Houghton, Mifflin, £ Co., Boston. 40 STUDIES IN PHYSIOLOGY 5. An organism, like the human body, is composed of organs, each doing its special work, yet all working together for the common good. Thus the hand supplies the organs of digestion with food ; the organs of digestion change the food into blood, some of which goes to furnish the hand with the materials it needs to do its work. THE FUNCTIONS ^CABRIED ON BY ALL PROTOPLASM 1. Taking in of food materials. 2. Change of food materials to protoplasm (assimilation). 3. Taking in of oxygen (respiration). 4. Oxidation of food materials to produce heat and other forms of energy. 5. Giving off of waste materials (excretion). CHAPTER IV A STUDY OF FOODS Why Foods are needed in the Body. — In our study of the composition of the body (pp. 16-19) we discussed the pres- ence of water, proteids, fats, carbohydrates, and mineral matters. We have learned, also, that in the presence of oxygen some of these materials are oxidized, thus forming the waste substances carbon dioxid, water, and urea. Hence, if the body is to continue its activities, there must be a con- stant supply of new material. This supply we obtain in our foods. Definition of a Food. — The three most important uses of foods were suggested on p. 30 in the preceding chapter. Hence we may say a food is any substance that yields material for the repair or growth of the body, or that supplies the fuel used by the body for producing heat or poiver to do work. 1. THE COMPOSITION OF FOODS Nutrients. — Our common foods are made up of many different compounds. Bread, for example, is composed of water, salt, starch, sugar, fats, and proteids. Over 80% of butter is fat; the other 20% is largely water and salt. These ingredients of food that can be used by the body are called nutrients. They may be classified as follows : (1) proteids (known also as albuminous and nitrogenous foods), (2) fats (and oils), (3) carbohydrates (starches and sugars), (4) min- eral matters, and (5) water.1 1 By some writers water is not regarded as a nutrient. Since, how- ever, it is an essential constituent of protoplasm, it may well be named among the nutrients. 41 42 STUDIES IN PHYSIOLOGY Refuse. — In many foods there are ingredients which the body cannot use: for example, the hard part of bones, the peel of potatoes, and the shells of eggs and of oysters. These substances we call refuse. Explanation of Food Chart.1 — The folio wing chart (Fig. 13) shows the percentage of each nutrient in several kinds of food. The first line of figures at the top of the chart and the vertical lines below them divide off the various per- cents ; for example, 10%, 20%, 70%, etc. In preparing the first line of the chart (which shows the composition of round beef with bone) a large number of analyses of meat were made and averaged. In each analysis a slice of round beef with the bone was carefully weighed. The bone was then removed, and found to constitute about 7% of the original weight of the meat. This fact is shown 011 the chart by the length of the black line representing refuse, which extends from 93% to 100%. The meat itself was then thoroughly dried to remove the water, and when the residue was weighed, and the various analyses were com- pared, it was found that water averages over 60% of this cut of beef (represented on the chart by the double oblique lines extending from about 33% to 93%). The proteids and fats were separated by special methods, and the mineral matters were obtained as ash by burning the beef. The chart then shows that something over 19% of round beef consists of proteids, about 12% is fat, and 1% more or less is mineral matter.; while, as already noted, there is 60% of water, and something over 7% of refuse and other indigestible matter. 1 The United States Government has provided for an extensive in- quiry into the food and nutrition of man. The work, done imder the authority of the Department of Agriculture in Washington, has been in charge of Professor W. O. Atwater of Wesley an University, Middletown, Conn., in whose laboratory the enterprise was begun and some of the most important part of the work has been done. The practical results of this inquiry are published by the Department of Agriculture* in the form of popular bulletins (see p. 60). Figures 13, 15, 16, 17, and 18 were copied from these publications. A STUDY OF FOODS 43 ^PROTEIDS FATS MUSCLE MAKING FUEL INGREDIENTS DRATES MATTERS NbTRiENTS BE™E NUTRIENTS- FIG. 13. — Percentage of the Nutrients in Foods. Percentage of Nutrients in Foods. — By looking at the chart1 one can easily compare the percentage of the nutri- ents in the given foods. In the composition of beef, 1 See " Laboratory Exercises," No. 16, A. 44 STUDIES IN PHYSIOLOGY mutton, and beans nearly 20% is seen to be proteids, while butter and potatoes contain less than 2%. The percentage of fat is high in butter (about 80 %) and in many other animal foods ; it is hardly present at all, however, in the foods derived from plants. On the other hand the carbohy- drates (starches and sugars) are usually wanting altogether in animal foods, but they constitute a large percentage of the foods of vegetable origin. 2. TESTS FOR THE NUTRIENTS With the help of a few chemicals and simple apparatus it is easy to determine the presence or absence of each kind of nutrient in a given food. These tests are as follows : — Tests for Proteids.1 — (1) Many proteid substances, like white of egg and lean meat, when heated, are coagulated or hardened into a solid mass. (2) If the temperature is raised still higher and these foods are scorched, a peculiarly unpleasant odor -is noticed, which may be compared to that of burning feathers. (3) One of the best methods of de- monstrating the presence of proteids is by the use of nitric acid and ammonia. Some of the food to be tested is placed in a test tube, concentrated nitric acid is added, and the mixture is warmed. If the food changes to a yellow color, we may be sure of the presence of proteids. After wash- ing the egg with water and adding concentrated ammonia, we find that the yellow color changes to a deep orange. Tests for Fats.2 — (1) A simple method of testing a given food for fats is by heating a small quantity, and then placing it on a piece of paper. If fat is present, it will make a translucent grease spot on the paper. (2) Ether or benzine,3 when poured upon foods, dissolves the fats, and 1 See " Laboratory Exercises," No. 11. 2 See " Laboratory Exercises," No. 12. 8 Caution ! Ether or benzine must never be used near a flame or a hot stove, since the vapor of these substances is very inflammable. A STUDY OF FOODS 45 when these solvents evaporate, the fat or oil is left be- hind. (3) A solution of osmic acid l stains fats brown or black. Test for Starch.2 — An iodine solution3 always turns starch blue. If a large amount of starch is present in a food that is being tested, a deep-blue color is produced upon the ad- dition of a few drops of iodine ; if the percentage of starch is small, the color will be light blue; the absence of a blue color shows that starch is not present. Test for Grape Sugar.4 — Many different kinds of sugars are found in foods; for example, cane sugar, beet sugar, sugar of milk, and grape sugar. These sweet substances differ more or less in chemical composition. In our physio- logical study, grape sugar is the most important, and its presence can be proved in the following way. A little of the given food is put into a test tube, and hot water is added to dissolve the sugar if present. Some blue Fehling's solu- tion 5 is then added to the mixture in the test tube, and the 1 Osmic acid is very expensive, and does not keep well in solution unless the bottle in which it is contained is perfectly clean and is Kept in the dark. A 1% solution gives more satisfactory results. 2 See "Laboratory Exercises," No. 9. 8 A quart (1000 cc.) of iodine solution is made by dissolving in 5 tea- spoonfuls (40 cc.) of water one half teaspoonful (4 grams) of potas- sium iodide and one fourth this amount (1 gram) of iodine. This solution, when thoroughly mixed, should be diluted to make one quart (1000 cc.). In a clean bottle this mixture will keep indefinitely. — From "Laboratory Exercises." Henry Holt & Co. 4 See " Laboratory Exercises," No. 10. 6 To make a quart (1000 cc.) of Fehling's solution, dissolve 3 tea- spoonfuls (35.64 grams) of pure copper sulphate (blue vitriol) in a little less than a half-pint (200 cc.) of water. Make a second solution by dissolving in a pint (500 cc.) of water twelve heaping teaspoonfuls (150 gr.) of Rochelle salt and 3 (5-inch) sticks of caustic soda (50 grams). Mix the two solutions thoroughly, and dilute with enough water to make a quart (1000 cc.). Fehling's solution does not keep for any great length of time, and hence must be made up fresh a short time before it is needed. It is more convenient to prepare it in small 46 STUDIES IN PHYSIOLOGY whole is boiled. If grape sugar is present, the blue Feh- ling's solution will be changed to a yellow, a deep orange, or a brick-red color ; if it is not present, none of these colors will be formed. Test for Mineral Matters.1 — The test for mineral matters has been already suggested in connection with the match experiments. If, when foods are burned, ashes are left behind, we may conclude that mineral matters are among the ingredients of the foods we are testing. Test for Water.2 — The water, found in varying quantities in all foods, may be obtained by putting the food into a closed dish, from which passes out a delivery tube like that used in the distillation of alcohol. When the dish is heated, the water is driven off as vapor. This is cooled as it passes through the delivery tube, and falls in drops. The percentage of water may be determined, as in the case of the round beef, by weighing the food before and after drying. Pure Food Laws. — One of the most important laws passed by the 59th Congress of the United States was that which compels every manufacturer of foods or medicines to state on the label the composition of each. Analysis of foods and drugs have proven that hitherto many of them were largely adulterated by cheap and often injurious compounds, put in to increase the manufacturers' profits. Then, too, as already stated, many patent medicines contain high per- centages of alcohol and other dangerous drugs. Under the new law the purchaser, if he takes the trouble to read the quantities from the tablets that can be obtained from druggists, or from John Wyeth & Brothers, Chemists, Philadelphia. Before making any tests, boil a small quantity of the Fehling's solution in a clean test tube. If it retains its transparent blue color, it is ready for use ; otherwise a fresh supply must be prepared. — From "Laboratory Exercises." Henry Holt & Co. 1 See "Laboratory Exercises," No. 13. 2 See "Laboratory Exercises," No. 8. A STUDY OF FOODS 47 printed label, should be able to determine exactly what he is paying for and putting into his body. 3. How PLANTS MANUFACTURE FOOD MATERIALS Carbohydrates. — A glance at Fig. 13 shows that carbohy- drates are found almost wholly in foods of vegetable origin. These starches and sugars are probably the simplest form of organic food manufactured by plants. We shall now try to understand something of the method by which plants carry on their all-important work. Organs of a Plant. — The common plants with which we are familiar — for example, dandelions, and maple trees — consist of three important organs, namely, roots, stems, and leaves. The root system is usually found beneath the ground, firmly holding the plant to the soil. Stems, on the other hand, commonly rise into the air in a more or less vertical direction, and serve as a means of connection between the roots below and the leaves that are attached along the sides and at the top of the plant. If one cuts off from a .living plant a small leafy branch, and puts the lower end of the stem into red ink, he will see after a time traces of the red ink in the veins of the leaf; and if the experiment is success- ful, every one of the fine branches of the veins will at last be filled with the colored fluid. Cross and longitudinal sec- tions of the stem will show that the red ink has been carried up through little tubes called ducts. If pieces of root are experimented upon in the same way, similar ducts will be found. We can demonstrate in this and in other ways that there is a continuous system of ducts, beginning at the tips of the roots, running up the stem, and branching out into the leaves. By this means water and the mineral matters dissolved from the soil are carried up the stem and supplied to the leaves. Leaves, as we all know, are usually green in color. When we examine the cross section of a leaf under the microscope, 48 STUDIES IN PHYSIOLOGY (see Fig. 14) we can make out a multitude of minute rec- tangular objects, the leaf cells, each being surrounded by a thin wall of woody material. Within each cell-wall there are numerous minute green masses known as chlo'ro-phyll bodies (from Greek, meaning leaf green). These chlorophyll bodies are grains of the cell protoplasm, having a peculiar green substance, by the help of which they are enabled to carry on the manufacture of starch in the presence of sunlight. Starch Manufacture. — For the manufacture of starch, the raw materials, carbon, hydrogen, and oxygen, must be fur- nished to these chlorophyll bodies. The water (H20) that — epidermis covering upper surface of the leaf. leaf cells containing green chlo- rophyll bodies. — epidermis covering lower surface of the leaf, stoma (one of the openings through the epidermis into the interior of the leaf). FIG. 14. — Cross section of a leaf very much magnified. comes up from the roots supplies the necessary amount of hydrogen and oxygen. The carbon is obtained from the carbon dioxid found in the air. The latter passes into the leaf through the outer layer of cells by means of many little openings or mouths known as sto'ma-ta (Greek sto- mata = mouths). In some unknown way the chlorophyll bodies, when acted upon by sunlight, are able to separate the carbon dioxid into oxygen and carbon and to cause the carbon thus obtained to unite with the hydrogen and oxygen * 1 The whole process may be represented by a formula something as follows : — A STUDY OF FOODS 49 of the water brought up from the roots. Plants, therefore, in manufacturing food materials that are useful to animals, take the waste carbon dioxid and water that are thrown off from animal bodies, and give in exchange free oxygen, which is essential for animal life. Hence, without plants animal life would soon cease to exist. FIG. 15. — The Potato Plant, showing Potato (shaded dark) from which Plant has grown ; also the New Growth of Stems, Leaves, and Potatoes. Storage of Starch and Sugar. — We shall see later that in the human body starch can easily be changed to sugar. In plants, too, a similar process is carried on, and sugar can also be changed to starch. Some of these carbohydrates, as soon as they are made, are used by the plant for the pro- 6 parts carbon dioxid + 5 parts water give 1 part starch + 12 parts oxygen. Or 6 C02 (= C6Oi2) + 5 H2O (= H10O5) give 1 C6Hi005 + 12 O. This means that for every six parts of carbon dioxid, five parts of water are needed. During this process a large amount of oxygen (equivalent to all the oxygen in the carbon dioxid) is given back to the air. 50 STUDIES IN PHYSIOLOGY duction of energy and in the process of growth. In many plants, however, considerable quantities are stored away for future use. In the potato plant, for instance (see Fig. 15), a great amount of the starch manufactured in the leaves is changed to sugar, is carried down beneath the ground through the tubes in the stem, and is there stored away as starch in the swollen tubers that we call potatoes. In a similar way sugar is collected below ground in the beet root and above ground in the stem of the sugar cane. Proteid Manufacture. — Proteids, as we have already learned (p. 18), are among the most complex of chemical compounds. In addition to the carbon, hydrogen, and oxygen found in the carbohydrates, the proteids contain nitrogen and sulphur, and sometimes phosphorus and other elements are present. It is very probable that plants make proteids out of carbo- hydrates, the additional nitrogen, phosphorus, and sulphur being furnished by the materials that are carried up from the soil by the sap. 4. USES OF THE NUTRIENTS The processes by which foods are changed into protoplasm and by which they supply the body with heat and muscular energy are extremely complex. Much study, however, has been given to the subject, and we are now reasonably sure as to some of the uses of the different nutrients. Uses of Proteids. — We have learned that proteid is the most important substance found in protoplasm. This class of nutrients is therefore essential for the growth and repair of muscle, nerve, and all the other body tissues. It is clear, then, that milk, meats, bread, beans, peas, oatmeal, and other foods that contain considerable amounts of proteid must be of first importance in the nutrition of the body, especially during its period of growth, although, as we shall see later, it is probably true that the average adult eats more than is necessary of this kind of nutrient. Proteids can A STUDY OF FOODS 51 also be oxidized in the body, and give heat and muscular energy ; but the chief fuel nutrients of food will be discussed in the next section. Uses of Fats and Carbohydrates. — Some of the fat we eat is stored away as fatty tissue and kept for future use. This tissue gives a plump outline to the body, acts as a cushion for many organs, and helps to keep our bodies warm by pre- venting the heat from escaping, and by being oxidized as it is needed. Much of the fat in our foods, however, is prob- ably oxidized to furnish heat and power without being stored within the body, and this class of nutrients furnishes fuel in a most concentrated form. This is the reason why the inhabitants of cold countries eat such large quantities of fatty foods. The starches and sugars of bread, potato, fruits, and milk are also used as fuel. Portions of the car- bohydrates are changed, too, into fat tissue and stored as a reserve of fuel. Comparison of Uses of the Nutrients. — We have seen that all of the nutrients thus far studied can be used to supply the body with energy. If our diet is deficient in any one, the others supply the need, and are burned instead. For growth and repair, however, proteids are absolutely essen- tial ; neither sugar, starch, nor fat can be transformed into this essential ingredient of protoplasm. An animal soon dies if it is not supplied with a certain amount of proteid. The Relative Fuel Values of the Nutrients. — We have made frequent reference to the use of food in giving energy to the body. By means of an apparatus called the cal-or-im'e-ter (Latin color = heat -f- metiri = to measure) it is possible to determine the amount of heat that each kind of nutrient will produce, or, in other words, to measure its fuel value. As we measure the quantity of food by the pound or quart, so its fuel value is computed in heat units or cal'o-ries. For 1 A calorie is "the quantity of heat necessary to raise the temper- ature of a kilogram of water from 0° to 1° centigrade." — Century Dictionary. 52 STUDIES IN PHYSIOLOGY practical purposes a calorie1 may be roughly described as the amount of heat required to raise the temperature of a pound of water through four degrees Fahrenheit. The fuel value of one pound of each of the nutrients is as follows : proteids, 1820 calories ; carbohydrates, 1820 calories ; fats, 4040 calories. On comparing these figures, we see that proteids and carbo- hydrates have equal value in generating heat, while the fuel value of fat is two and a half times as great. The heat-producing power or fuel value of each of the foods (in Fig. 13) is indicated by the narrow black line ; the second row of figures at the top of the chart (400, 800, etc.) repre- sents the number * of calories. Thus the fuel value of a pound of milk is about 300 calories ; a pound of butter, on the other hand, will generate nearly 3500 calories of energy. Uses of Mineral Matters and Water. — The mineral mat- ters like the phosphates of lime and magnesium are neces- sary for making bone. Salt is used in large quantities by all civilized nations ; it makes foods more palatable, and it is important in the processes of digestion. Water, as we have learned, is an essential constituent of protoplasm, and hence the body needs it constantly. A large amount is supplied by the water contained in our solid foods, and we get the rest from the milk, tea, coffee, and from the water that we drink. 5. COOKING OF FOODS Importance of Proper Cooking. — Some of our foods, like milk, nuts, and fruits, are eaten without being cooked. The great majority, however, before they are taken into our bodies are changed considerably. It is important for us to learn the essential principles of good cooking, since food, as often prepared, loses much of its flavor, becomes more or less indigestible, and is deprived of a considerable percent- age of its nutrition. Methods of cooking Meats. — In civilized communities meats are rarely eaten raw. They are usually cooked by broiling, A STUDY OF FOODS 53 roasting, boiling, or frying. Frying involves the use of fats. Since the average American is said to eat too much fat, and since frying tends to make foods indigestible, this is doubt- less the poorest method of preparing meat, and hence we shall not discuss it further. Reasons for cooking Meats. — The reasons for cooking meat are these : (1) proper cooking loosens and softens the fibers, thus preparing the meat for mastication and for the action of the digestive juices ; (2) heat kills the bacteria and other parasites (tapeworms and roundworms or trichina) that are sometimes found in foods of animal origin; (3) cooking makes the meat more attractive in appearance and often improves its flavor ; and (4) cooked meat is more completely digested. It is probably true, however, that raw or partly cooked meats are more easily digested ; for this reason rare meat is usually given to invalids. Soups. — If we wish to obtain nutritious soups, the meat should be cut into rather small pieces and first put into cold water to which a little salt has been added. A small proportion of the albuminous substances, and large amounts of so-called "extractives," or flavoring matters, are drawn out by the water and salt, and since the meat is in small pieces, a considerable proportion of the mineral matters is thus dissolved. When we warm the mixture, we cause the fats to melt, and when it is boiled, much of the tough con- nective tissue is made more or less soluble by being turned into gelatin. The soups thus obtained, which are rich in proteids, fats, and mineral matters, are made more palatable by the addition of vegetables and condiments. The meat which is left after the soup has been prepared is, of course, more or less tasteless. Only small percent- ages, however, of the nutrients have been withdrawn ; hence the soup meat should not be thrown away, but should be used for making hash, as described on p. 59. Boiling Meats. — When the meat itself is to be eaten, and the broth is not to be used, the whole piece should be plunged 54 STUDIES IN PHYSIOLOGY into boiling water for a few moments. In this way the albumin on the surface is quickly coagulated, and the crust thus formed prevents the loss of the meat juices. The temperature of the water should then be reduced somewhat below the boiling point by pushing the kettle toward the bapk of the stove, and the meat should then cook slowly until it is done. A piece of meat, when cooked in this way, is tender and juicy throughout. If, however, the water is kept at the boiling point (212° F.), the meat can be easily torn apart, but the fibers are found to be hard and stringy. Stewing. — It is unfortunate that meat stews are not more highly regarded in American families, for by this method of preparing meat all its nutritive ingredients are used. To make a good stew the meat should be cut into rather small pieces and placed in cold water. Some of the flavoring mat- ters and soluble albumins pass out into the broth, making it rich and nutritious. When the stew is allowed to simmer for several hours on the back of the stove, the meat itself becomes tender and readily digestible. The addition of vegetables makes it a most nourishing and palatable dish. Roasting and Broiling. — The best method of cooking meat, if the broth is not desired, is by roasting or by broiling, since smaller percentages of the nutrients are lost than is the case in boiling. The outer layer of albumin must, however, be coagulated at once, and for this purpose a very hot fire is needed. When the piece to be roasted is small, the high temperature should be maintained until the meat is cooked. A large roast, on the other hand, after the outer covering has been coagulated requires a slower fire and a longer time; meat is not a good conductor of heat, and a hot fire would scorch the outside before the central mass could become thoroughly heated. A better crust is formed on. the outer surface of the roast if the meat juices (mostly fat) in the pan are frequently poured over the surface of the roast. This is called "basting." Reasons for cooking Vegetables. — The starches, which we A STUDY OF FOODS 55 have learned are present in large quantity in foods of vege- table origin, are usually inclosed in cells, the walls of which are formed of indigestible cellulose. Hence, before starch can be digested, it must be freed from this cellulose envelope. This is largely accomplished by cooking, which causes the starch grains to swell. The cell walls are broken open in this way, and when the grains burst, a larger surface is ex- posed to the action of the digestive juices (Figs. 16 and 17). This is strikingly shown in popping corn. The crust of bread is more easily digested than the softer parts, and toasting bread increases still further its digestibility, because this browned starch (sometimes called soluble starch) requires less change before it can be used by the body. Boiling Vegetables. — Experiments have shown that a good deal of nutrition is lost by boiling vegetables in water. Much of this waste can be avoided, however, if one heeds the following directions : (1) Vegetables should be cooked as far as possible in their peels, for these outside coverings keep the sugar, proteids, and mineral matters from being FIG. 16. — Cells of Raw Po- tato with Starch Grains inclosed in the Cellulose Walls. FIG. 17.— Cells of a Potato well steamed and mashed. Starch Grains have been burst by the Heat. drawn out by the water; (2) if, however, the vegetables must be peeled and cut up, the pieces should be as large as possible, as a smaller surface is thus exposed to the water; (3) the amount of water should be as small as 56 STUDIES IN PHYSIOLOGY possible, and the vegetables should be cooked rapidly, in order to give less time for the solvent action to take place. Bread Making. — When bread is made, water (or milk), butter, salt, sugar, and yeast are added to flour. After the mixture has been stirred together, a sticky mass of dough is formed, which in a warm place begins to rise. This is due to the fact that the yeast cells change the sugar into alcohol and carbon dioxid. Bubbles of gas are thus imprisoned in the sticky dough. While expanding and seeking to escape, they make the solid mass porous. After the bread has risen sufficiently, it is kneaded in order to break up the large bub- bles and in order to distribute the gas throughout the dough. When the bread is baked, the alcohol and carbon dioxid pass off into the air, leaving the bread light and digestible. 6. DAILY DIET Diet required by Americans. — Many investigations have been carried on, in this country and in Europe, to determine the amount of each kind of nutrient needed per day for the work of the body. The conclusions that were drawn from this study are represented on the lower two lines of Fig. 18. According to these conclusions the average American, when at moderate work, requires about one fourth of a pound of proteids to provide for the growth and repair of the body, and a quarter of a pound of fat and a pound of carbo- hydrates to furnish the needed energy. This is about the amount eaten by a man of average appetite. Recently, however, at the Scientific School of Yale Uni- versity, some very careful experiments have been performed by Professor Chittenden which seem to prove conclusively that this pound and a half of solid nutrients for each day is considerably more than what the body really needs. Dr. Chit- tenden experimented on five of the Yale University profes- sors, on thirteen soldiers of the United States army, and on five of the best athletes at Yale ; he found that all agreed they could do better physical and mental work, and that, too, A STUDY OF FOODS 57 without any loss of weight, when they had become accus- tomed to taking less than half their ordinary amount of food. In several instances rheumatism, biliousness, and other derangements of the body were cured by this restricted diet. " There is no question, in view of our results," says Professor Chittenden, that people ordinarily consume much more proteid food than there is any real physiological necessity for, and it is more than probable that this excess of food is in the long run detrimental to health, weakening rather than strengthening the body, and defeating the very objects aimed at." Necessity for a Mixed Diet. — By comparing the proportions of the nutrients suggested for the daily diet with the com- position of the various foods given in Fig. 22, one sees that in none of them are the nutrients in the right proportions. Cow's milk comes the nearest to being a perfect food, but its percentage of carbohydrates is too small; if we were to feed upon meat alone, we should get too large an amount of proteid s; while most of the vegetable foods supply an ex- cessive amount of carbohydrates. Hence, a well-balanced diet should consist of a mixture of many kinds of foods, a conclusion that agrees with our everyday experience. Vege- tarians may be right in their contention that all the nutritive elements of food are found in vegetables, but the great pro- portion of the human race doubtless secure a far more healthful diet by combining the animal proteids and fats with the carbohydrates furnished by plants. 7. FOOD ECONOMY1 Importance of Food Economy. — It is said that in a large proportion of American families more than half of the total income is spent for food, and that rent, fuel, clothing, and all other expenses must come from the remainder; hence the importance of the study of food economy. The average American, however, is far from economical in the matter of 1 See "Laboratory Exercises," No. 16, B. 58 STUDIES IN PHYSIOLOGY PROTEIDS FATS CARBOHYDRATES BEEF, ROUND BEEF, SIRLOIN HAM, SMOKED SALT PORK, VERY FAT CODFISH, FRESH CODFISH, SALT MACKEREL, SALT OYSTERS, 35 CTS. QUART EGGS, 25 CENTS DOZEN MILK, 7 CENTS QUART CHEESE, WHOLE MlLK CHEESE, SKIM MILK WEIGHTS OF NUTRIENTS AND CALORIES OF ENERGY IN 25 CENTS' WORTH. 6000 CAL. I m I , I <1 I I BS. CAU WHEAT FLOUR WHEAT BREAD STANDARD FOR DAILY DIET FOR 1 MAN AT MODERATE WORK t ATWATER FIG. 18. — Pecuniary Economy of Foods. foods ; in the first place Tie wastes money in buying foods, and in the second place wastes the nutrients he has bought. A STUDY OF FOODS 59 Economy in the Purchase of Foods. — We have already suggested that smaller quantities of food should be eaten by the average American, and this is especially true, so far as animal proteids are concerned, for meats are the most ex- pensive kind of food. If this plan were followed, a large saving in the year's expenses could be effected. Fig. 18 shows the weights of different food materials that can be purchased for 25 cents. On comparing the two meats at the top of the chart, one can see that a greater fraction of a pound of solid nutriment can be obtained by spending 25 cents for round steak than could be secured by the purchase of sirloin. Yet the latter is bought even in very poor fami- lies, possibly because of the mistaken idea that higher prices insure more nutrition. From oysters one gets less of the nutrients than from any other food represented on the chart ; hence, if one's income is small, this kind of food should be regarded as a luxury, seldom purchased except in case of sick- ness. Among the best foods for the growing boy are graham or corn-meal bread, the cereals (oatmeal, rice, etc.), milk, meat, fruit, and fish ; they are economical and furnish the required nutrients in a form that can be easily digested. Waste of Food. — In discussing the cooking of foods, we suggested some of the ways by which the loss of nutritive ingredients can be prevented. We waste foods, however, in other ways ; for instance, we often throw away bones and gristle, regardless of the fact that they contain a consider- able percentage of proteids, gelatin, and fat from which one might make a nutritious soup. It has been found that large proportions of the food materials still remain in a piece of meat after it has been used for soup. A most delicious and healthful hash could be prepared by chopping this soup meat and combining it with vegetables. The garbage pails of most kitchens receive far too large a percentage of the food that is bought for the household, and many a dollar would be saved for other purposes if more care were exer- cised to prevent this waste. 60 STUDIES IN PHYSIOLOGY The food problem, then, for the healthy human being is this — how to obtain the largest amount of good, nutritious food for the least money. To this problem an intelligent individual, if he can be led to see the importance of the sub- ject, will devote considerable thought. This problem can- not be solved, as we have seen, by consulting market prices, for often the highest-priced foods contain small percentages of the nutrients. Neither can we be sure of a good supply of foods by following our tastes. To many people cakes and sweetmeats are more appetizing than sandwiches and cereals. Yet it is the latter that supply the all-essential proteids. The composition of various foods can be found only by chemical analysis, and their nutritive value can be deter- mined only by experiment. Fortunately these analyses and experiments are being carried on by the United States government. The results are published in the Bulletins of the Department of Agriculture, Washington, D.C., many of which will be sent free to any address. The most sug- gestive of these publications are " Foods : Nutritive Value and Cost " ; " Meats : Composition and Cooking " ; " Milk as a Food"; "Fish as a Food"; "Sugar as a Food"; " Foods, and the Principles of Nutrition." A STUDY OF FOODS 61 REVIEW OF FOODS NAME OF NUTRIENT TEST FOR NUTRIENT USES OP NUTRIENT FOODS CONTAINING NUTRIENT Proteid (albumin, nitrogenous food). Coagulates when heated. Smells like burn- ing feathers when scorched. Turned to orange color by nitric acid and am- Necessary for the manufac- ture of pro- toplasm. When oxidized produces energy. Meat, eggs, milk, cheese (among animal foods) , and beans, peas, oatmeal (vege- table foods). monia. Starch. Turned to a blue color by iodine solution. Produces energy. Transformed into fat. Vegetable foods (especially cereals). Sugar. Fehling's solu- tion is turned orange or red when boiled with grape Produces energy. Transformed into fat. Vegetable foods (especially fruits) ; milk sugar is found in milk. sugar. Fats (or oils). Make grease spots on paper. Dissolved by ether or ben- zine. Turned brown or Produce energy. Transformed into body-fat. Animal foods (especially butter, pork, cheese), nuts, cocoa, chocolate. black by osmic acid. * Mineral matters. Left as ash after food is burned. Help to form bone and Common salt; mineral matters other tissues. Aid in digestion. in most vege- table and ani- mal foods. CHAPTER V A STUDY OF STIMULANTS, NARCOTICS, AND POISONS 1. DEFINITION OF STIMULANT, NARCOTIC, AND POISON Definition of a Stimulant. — In the preceding chapter we have discussed those substances that yield material for the repair or growth of the body, or that supply the fuel used by the body in producing heat or power to do work. But in addition to the various nutrients that can be used for one or all of these purposes, we often take with our foods cer- tain substances that are not used in any of these ways. For example, pepper, mustard, vinegar, tea, and coffee never be- come a part of our living substance, nor are they consumed in any considerable amount to supply us with energy. Hence, we cannot regard these compounds as foods. Most of them, however, add an agreeable flavor to our foods, and so stimulate our appetites and aid in the digestion of the real nutrients. Most of these compounds, also, do no harm in our bodies if taken in moderate quantities, and so we cannot regard them as poisons ; for the Century Dictionary defines a poi- son as " any substance which, introduced into the living organ- ism directly, tends to destroy the life or impair the health of that organism" We are considering, then, a class of substances that are neither foods in a strict sense, nor are they poisons. This sort of compounds we call stimulants. A stimulant is any agent that temporarily quickens some process in the body. When we wish to quicken the activities of a horse, we touch him more or less with a whip, which acts like a stimulant. 62 STIMULANTS, NARCOTICS, AND POISONS 63 And in a similar way we may rightfully use some of the substances we have named above, if we make sure that we use these stimulants in moderation.- We should always re- member, however, that a stimulant causes only temporary increase of activity, and that if we apply it too frequently or in too great quantity to a horse or within our bodies, it soon loses its power to bring about even a temporary in- crease of activity, and that then it comes to do absolute harm. Definition of a Narcotic. — Another class of substances that we sometimes use has an effect directly opposite to that of stimulants. Ether, morphine, and chloroform, for example, do not quicken any process in the body, as do stimulants, but on the contrary lessen the degree of activity. Hence, instead of comparing the action of such substances to that of a whip on a horse, we may liken them to the bit and reins when they are used to check the motions of the animal. Any compound that acts in this way is called a narcotic, which we may define as " any substance that directly induces sleep, blunts the senses, and in large amounts produces com- plete insensibility" The terms stimulant and narcotic that we have just de- fined naturally suggest a discussion of the use and abuse of tea and coffee, tobacco and alcohol, and to that discussion we will now turn. 2. TEA AND COFFEE Use and Abuse of Tea. — " Tea should be used only in the form of an infusion, made by pouring boiling water upon the right amount of tea leaves, and allowing it to stand a short while to l draw.' ': For this purpose about a spoon- ful of tea should be used to every cup of water. Tea should never be put on the stove to boil, for two reasons : in the first place, by this treatment the delicate taste and odor are lost ; and, in the second place, if the tea infusion is boiled, the tea leaves give out a chemical known as tan'nin} which 64 STUDIES IN PHYSIOLOGY tends to injure the lining of the stomach. For these reasons, too, the tea " grounds " should never be used a second time for the preparation of tea. The finest and most delicate por- tion of a tea infusion is that which is poured off within three or four minutes, for this will be found to have the best flavor and the least of tannin and other harmful compounds. " When properly made, tea in moderation is a wholesome, agreeable, and refreshing stimulant beverage, particularly grateful in conditions of mental or physical weariness. Used in excess, it exerts a harmful influence upon the ner- vous system, arid in a too strong form injures the digestive organs." The foregoing remarks, quoted from Harrington's "Practical Hygiene," apply to adults rather than to growing children and youths; for in early life stimulants of every kind should be avoided as much as possible, as they tend to interfere with the healthful development of protoplasm. We should remember that tea is in no sense a food, and so cannot be of use in repair or growth of tissue; both of which functions are of prime importance during the first twenty years of life. Use and Abuse of Coffee. — Most that has been said in regard to tea applies equally well to coffee, except that in its preparation the infusion should be put on the stove and allowed to come to a boil; it should then be put on the back of the stove until used. "Coffee acts as a decided stimulant to the nervous system ; it doubtless enables adults better to perform hard work, and diminishes for them the sense of weariness; " but in the diet of a growing child, both tea and coffee should be used very sparingly, if at all, since they simply excite the organs to unnecessary activity. 3. TOBACCO Effect of Tobacco on Growth. — In discussing the effects of tobacco, it is important, as was the case with tea and coffee, to distinguish between the results of its use by the young STIMULANTS, NARCOTICS, AND POISONS 65 and by adults. Just because his father seems to be using tobacco without apparent harm is no reason why a boy can safely smoke. We have already called attention to the com- plex composition of protoplasm. During the whole period in which the body is attaining its growth this living sub- stance is affected far more appreciably and seriously by the use of stimulants and narcotics than is the case later in life. Tobacco is a narcotic in its effects, that is, it tends to decrease activity and likewise growth. That such is its effect during early life has been abundantly proven in many ways. But perhaps the most conclusive facts are those presented by actual measurements made in college gymnasiums. Dr. Hitchcock of Amherst College, who has made careful measurements of college students for a good many years, finds that those who do not smoke increase in height during their college course 37% more than those who do smoke, and in chest girth this difference is 42% or nearly one half as much again. Dr. Seaver of the Yale Gymnasium finds also that in height and lung capacity smokers are considerably inferior to those who do not use tobacco. " Whatever difference of opinion there may be regarding the effect of tobacco on adults — and much difference of opinion exists — there is almost complete agreement among those best qualified to know that the use of tobacco is in a high degree harmful to children and youths. Physicians, teachers, and others who have much to do with boys very generally remark that those who begin to smoke at an early age very seldom amount to much. Andrew D. White, former President of Cornell University, sums up the matter as fol- lows: ' I never knew a student to smoke cigarettes who did not disappoint expectations, or, to use one expressive ver- nacular, " kinder peter out." I have watched this class of men for thirty years, and cannot recall an exception to this rule. Cigarette smoking serves not only to weaken a young 66 STUDIES IN PHYSIOLOGY man's body, but also to undermine his will and to weaken his ambition.' r' Tobacco and Athletics. — One of the rules rigidly enforced in athletic contests is that all candidates must abstain from the use of tobacco while in training. The reason for this insistence is the fact that tobacco seriously interferes with the action of the lungs and heart; hence, those who smoke are found to be easily " winded " in the games. 4. ALCOHOL Alcohol as a Possible Food. — Like the carbohydrates and fat, alcohol is composed of carbon, hydrogen, and oxygen.1 Since it contains no nitrogen, it has no value in the processes of growth and repair; in other words, it cannot be made into protoplasm. It cannot, therefore, in any sense, like meat, milk, and eggs, answer as a complete food. Alcohol we know can be burned or oxidized in stoves or lamps for the production of heat, and doubtless in a few years this kind of fuel will be widely used for generating mechanical energy in various kinds of engines. Professor Atwater has shown that alcohol also, if used in sufficiently small amounts, may produce within the human body a cer- tain amount of heat and muscular power. Indeed, in some cases of extreme weakness, especially in diseases, alcohol is regarded by some eminent physicians as necessary for sav- ing life. Not all the leading writers on physiology, however, are in agreement as to any possible food value of alcohol, and the following quotations will show a wide diversity of opinion. Professor Adolph Tick: "We may unhesitatingly desig- nate as a poison any substance which, introduced into the blood in comparatively small amounts, causes disturbances 1 Its chemical composition is represented by the symbol CaHgOH. STIMULANTS, NARCOTICS, AND POISONS 67 in the functions of any organ. That alcohol is such a sub- stance cannot be doubted. ... It is when introduced into the blood oxidized, like a nutriment, to carbon dioxid and water, and this oxidization must, of course, like the oxidiza- tion of albumen, fat, or sugar, produce heat. . . . Although the relations of the oxidization of alcohol to that of the true nutriments in the animal economy have not yet received a complete physiological explanation, it is certain that alcohol, even when taken in moderation, cannot be classed among the useful nutriments." — "Die Alkoholf rage, " 2d ed., Dresden, 1895, pp. 2-6. G. Bunge: "We know that alcohol is mostly oxidized in our body. . . . Alcohol is therefore, without doubt, a source of living energy in our body. But it does not follow from this that it is also a nutriment. To justify this assumption proof must be furnished that the living energy set free by its oxidization is utilized for the performance of a normal function. It is not enough that potential energy is transformed into living energy. The trans- formation must take place at the right time and place, and at definite points in definite elements of the tissues. These elements are not adapted to be fed with every sort of oxidizable material. We do not know whether alcohol can furnish to the muscles and nerves a source of energy for the performance of their functions. ... In general, alco- hol has only paralyzing properties, etc." — "Lehrbuch der Physiologischen und Pathologischen Chemie," Leipzig, 1894, p. 124. T. Lauder-Brunton : "The conclusion to which all evi- dence points is that alcohol is a food, and in certain circum- stances, such as febrile conditions, it may be a very useful food; but in health, when other kinds of foods are abundant, it is unnecessary, and, as it interferes with oxidization, it is an inconvenient kind of food." — "Text-book of Pharma- cology, Therapeutics, and Materia Medica," London, 1887, p. 768. 68 STUDIES IN PHYSIOLOGY M'Kendrick: "If oxidized even to a small extent, and the evidence as indicated points to the oxidization of by far the larger proportion of it (95%), alcohol must be regarded in the scientific sense as a food. . . . While, therefore, it must be classed technically as a food, it is in many respects an unsuitable food and its place can be taken with great ad- vantage by other substances.7' — "Physiology," Glasgow, 1889, p. 19 (Vol. 2). Halliburton: "Alcohol is thus within narrow limits a food. ... It is, moreover, a very uneconomical food; much more nutriment would have been obtained from the barley or grapes from which it was made. The value of alcohol within narrow limits is not as a food, but as a stimulant, not only to digestion, but to the heart and brain." — "Text- book of Chemical and Pathological Physiology," 1891, p. 600. " We have, thus, one group of physiologists at the one extreme, who take grounds, more or less strongly, against any dietetic use or value of alcohol, even this group admit- ting that it is not fully proved that alcohol is not a food. We have a second group who are inclined to favor moderate dietetic use of alcohol, tending to class it with non-proteid foods, but still maintaining that its classification as a food is not clearly established. ... A third group of physiolo- gists and pharmacologists, whether they advocate or oppose its use, evidently consider recent discussions as to the food status of alcohol unnecessary quibbling. For them the evidence is sufficient to pronounce alcohol in moderate quantities a food." — "Physiological Aspects of the Liquor Problem." Houghton, Mifflin & Co., 1903. Alcohol as a Stimulant, a Narcotic, and a Poison. — Alcohol, then, may be regarded as having food value when prescribed by a physician in case of sickness, and doubtless it can be oxidized in the body to supply a certain amount of energy, if it is taken in small quantity and sufficiently diluted. But as ordinarily used in liquors, alcohol becomes almost always STIMULANTS, NARCOTICS, AND POISONS 69 either a stimulant or a narcotic, and it is for this purpose that it is taken, not for its possible fuel value. In later chapters we shall discuss the affects of alcohol on various organs of the body. One fact should, however, be continually emphasized, namely, that even if it should be proved that alcohol, when used by adults in moderation, may generate a certain amount of energy, still this is an exceedingly dangerous compound to introduce in any form into the diet of a boy or girl. In the first place, even more than tobacco, it interferes with the healthy growth of protoplasm ; and in the second place, the use of liquors in moderation by a great many people, both young and old, is absolutely impossible. Men never become drunkards, pau- pers, and criminals by taking the real nutrients, starch- sugar, fats, or proteids, nor does the taste for any of these foods become uncontrollable, as is so often the case with alcohol. " Till he has tried it, no one can be sure whether he can control his appetite or not. When he has ascer- tained the fact, it is often too late. The child should be taught to avoid alcohol because it is dangerous to him. The only certain safety for the young lies in. total ab- stinence." We have found, then, that the effects of alcohol on the body depend very largely upon the quantity taken ; if the amount is small, .alcohol may possibly be regarded as a source of energy, and hence, in a limited sense, as a food ; in larger amounts it increases temporarily the activity of the organs of the body, and then it becomes a stimulant ; if still larger quantities are taken, the narcotic effects of alco- hol are shown in complete intoxication ; and finally, a suffi- cient amount may be consumed to poison the organs and cause death. No one who begins the use of alcohol expects to take such an amount that it will act like a poison, or even as a nar- cotic. There is, however, a constant danger that he will do so. But even if he does not, the following quotations will 70 STUDIES IN PHYSIOLOGY show that moderate drinking is likely to injure one's chances in business and to shorten what insurance men call one's " expectation of life." Business Argument for Total Abstinence. — Eule 17, New York Central & Hudson Eiver R. R.: " The use of intoxicat- ing drink on the road or about the premises of the corpora- tion is strictly forbidden. No one will be employed, or continued in employment, who is known to be in the habit of drinking intoxicating liquor." Rule H, New York, New Haven & Hartford R. R. : " The use of intoxicants by employes while on duty is prohibited. Their habitual use, or the frequenting of places where they are sold, is sufficient cause for dismissal." Total Abstinence and Life Insurance.1 — " It is now becoming generally recognized that the alcohol habit is one of the main factors in determining length of life. No life office will knowingly accept the proposal of any one known as a hard drinker. Evidence of a very striking kind is rapidly accumu- lating which shows that even the moderate use of alcohol is prejudicial to health and longevity. In England about a dozen life offices recognize this fact in one of two ways : (1) By giv- ing a reduction of premium to abstainers, or (2) awarding them a larger share in the profits. The Scottish Temperance Life Insurance Company has, from its formation in 1883, worked its business in two sections, giving total abstainers a reduction of ten per cent in their premiums. Last year the Sun, one of the oldest life offices, established in 1810, opened a special section for abstainers, giving them a reduction of five per cent in their premiums. . . . The experience of all temperance life offices proves the enhanced vitality of total abstainers. This makes it evident that, when they are mem- bers of a general life office, abstainers have to pay more than their fair share toward meeting demands made by the higher death-rate of the non-abstainers." — London Spectator. 1 These quotations were furnished the author by the Equitable Life Assurance Society of the United States. STIMULANTS, NARCOTICS, AND POISONS 71 • " Ten years ago the American Temperance Life Insurance Association was formed in this city (K.Y.), and accepts nothing but total abstinence risks. It has had pronounced success, and has paid something like $ 200,000 in death claims. President Frank Delano states that the results of. their business show that the ratio of their death-rate to that of general risks is about 26 per cent in favor of the total ab- stainer." — WILLIAM E. JOHNSON. The Cost of Intemperance. — The following figures, compiled by the League for Social Service of New York City from the United States Census, present some very striking facts as to the cost to our country of the abuse of alcohol. During the year 1880 (and the same figures would doubtless hold true for any other year), it was found that three-fourths of all the pauperism, one-fourth of all the insanity, and three-fourths of all the crime in the United States were directly caused by intoxicating drinks. The Effect upon Dogs of Moderate Drinking of Alcohol. — During the years 1895 to 1900, Dr. Hodge of Clark Univer- sity, Worcester, Mass., carried, on some very instructive experiments upon dogs. He secured four spaniel puppies, all of which were born on Washington's Birthday, 1895 j the two males were brothers and the females sisters. Dr. Hodge carefully watched the four for nearly two months before be- ginning his experiments, in order to pick out the two most vigorous animals ; these he named " Tipsy " and " Bum," and then put in with their chief meal each day a moderate amount of alcohol ; it was not enough, however, to cause any evidence of intoxication. The other two spaniels, "Nig" and " Topsy," received no alcohol. For over five years these dogs were studied, and important facts were learned as to the general effect of alcohol on physiological processes. Early in his observations it became evident to Dr. Hodge that the dogs that were receiving the alcohol were far less playful than were those that had no alcohol in their food. To measure the comparative activity 72 STUDIES IN PHYSIOLOGY of the different animals he attached to the collar of each dog a Waterbury watch adjusted in such a way that it would tick once each time the animal moved, and so at six o'clock each day he could determine and set down the record made by each dog. He found that for a period of two months and more "Bum" was only 71% as active as "Nig," while "Tipsy" moved about only 57% as much as "Topsy "; in other words the two alcoholic dogs lost 25% to 50% of their activity. Bum. Tipsy. Nig. Topsy. FIG. 19. — The appearance of the four spaniels six months after the ex- periments were begun. (Copied from "Physiological Aspects of Liquor Problem," by permission of Dr. Hodge and of Houghton, Mifflin & Co.) A second series of experiments was made to determine the comparative endurance of the four dogs and their ability to accomplish things. The animals were all taught to retrieve a rubber ball when it was thrown the length of the gymna- sium floor, a distance of 100 feet. At each trial the ball was thrown 100 times, and a record was kept of all the dogs that STIMULANTS, NARCOTICS, AND POISONS 73 started for the ball and of the one that succeeded in bring- ing it back. When he had averaged a long series of experi- ments, Dr. Hodge found that " Bum " and " Tipsy " secured the ball only about half as often as did " Nig " and " Topsy " ; the two alcoholic dogs also gave evidence of much greater fatigue during the trials. " A very striking result of the entire research," says Dr. Hodge, " and one entirely unexpected on account of the small doses of alcohol given, has been the extreme timidity H'CMlV.CMil If 01 MA I PA ft t mij "• oobp €/*••"; OOOO.-V eecctt* C C • I 1 t i» ••• + . 3 It €• * Fia. 20. — Diagram showing Offspring of the Two Pairs of Dogs. of the alcoholic dogs. . . . While able to hold their own with the other dogs in the kennel, the least thing out of the ordinary caused practically all the alcoholic dogs to exhibit fear, while the others evinced only curiosity or interest. Whistles and bells, in the distance, never ceased to throw them into a panic in which they howled and yelped, while the normal dogs simply barked. This holds true of all the dogs that had alcohol in any amount." Another most striking result of the use of alcohol was 74 STUDIES IN PHYSIOLOGY shown in its effects on the young of " Bum " and " Tipsy." Of the 23 puppies descended from these alcoholic animals, only 17% lived to be normal dogs; the rest were either de- formed or unable to nourish themselves, and all died soon after birth. On the other hand, of the 45 young of " Nig " and "Topsy," over 90% were healthy puppies. (See Fig. 20.) Hence, the puppies of the dogs that took alcohol, even in moderation, were over Jive times as likely to die young as were the puppies born of abstaining parents. In the spring of 1897, in the course of these experiments, a great many dogs . throughout the city of Worcester were afflicted with distemper, and dogs sick with the disease were not uncommon on the streets. At that time, Dr. Hodge had in all five dogs that were taking alcohol and four that were not. It was found that there was a marked difference in the effect of the disease on the two classes of animals. All the alcoholic dogs, with the exception of the one that had taken the smallest amount, had the distemper with great severity ; all the normal dogs had it in the mildest possible form. Hence, we may conclude from these experiments that al- cohol, when given to dogs, even in moderation, (1) decreases their natural activity, (2) lessens their power of endurance and their ability to accomplish things, (3) decreases their power of resistance to disease, and (4) increases the percent- age of deformity and of death among their offspring. These conclusions have a most important bearing on the gen- eral subject we are considering, for statistics show that pre- cisely similar effects follow even the moderate use of liquor by human beings. CHAPTER VI A STUDY OF BLOOD MANUFACTURE Definition of Digestion. — In the preceding chapter we dis- cussed the composition of foods, the methods of cooking, and the uses of foods to the body. We shall now follow the changes that take place in these foods, for before the different nutrients can be supplied to the brain, the muscles, or the bones, they must be changed from a solid or semi-fluid condition into liquids that can be absorbed. This process is called digestion. It is carried on within our bodies in a complicated tube nearly thirty feet in length, which is called the al-i-men'ta-ry canal (Latin alimentum = nourish- ment). Digestion, then, may be defined as the series of changes within the alimentary canal by which food is made ready to become a part of the blood. Parts of the Alimentary Canal. — The alimentary canal be- gins at the mouth opening, enlarges to form the mouth cavity, and this in turn communicates behind with a somewhat smaller throat cavity. Posterior to the throat is the e-soph'a-gus or gullet, which conducts the food into an enlarged pouch, the stom'ach. Most of the lower half of the trunk is filled with the much coiled in-tes' tine, which begins at the stomach and opens to the outside of the body at the posterior end of the trunk. Digestive Glands. — Several important organs, called diges- tive glands, lie adjacent to the alimentary canal, but con- nected with it. They produce digestive juices, which flow into the food canal through small pipes or ducts. The sal'- i-va-ry glands pour their secretions into the mouth cavity. 75 76 STUDIES IN PHYSIOLOGY In the region of the stomach are the liver and the pan'cre-as. The former secretes bile and the latter pancreatic juice. Both of these digestive juices flow into the intestine in the FIG. 23. — Parts of the Alimentary Canal. region near its opening from the stomach. TJie alimentary canal may be regarded as a blood-making laboratory, in which our food is made liquid by the juices produced in the digestive glands. A STUDY OF BLOOD MANUFACTURE 77 1. THE MOUTH CAVITY 1 Walls of the Mouth Cavity. — The cavity of the mouth is inclosed at the sides by the muscles of the cheek. The roof of the mouth is formed by a horizontal plate of bone (easily felt by the finger or the tongue), called the hard palate. This separates the cavities of the mouth and nose. Near the back of the mouth the hard palate ends abruptly, and the partition between these two cavities is completed by the soft palate. The muscular tongue helps to form the floor of the mouth cavity. Mucous Membrane. — If, by the aid of a hand mirror, one looks within one's mouth cavity, one finds it lined with a soft, moist covering of a pink or red color. This is called mu'cous membrane. It is much thinner than the outside skin, and many blood vessels lie just beneath it. To these facts is due its red color. Much of the moisture that covers the inner lining of the whole alimentary canal is the slimy mucus secreted by the gland cells of the mucous membrane. 2. THE TEETH2 Arrangement of the Teeth. — Within the mouth cavity the solid food is cut into small pieces, mixed with the juices of the mouth, and then ground into a pulpy mass. A large part of this work is done by the teeth, which are arranged in two semicircular arches. They are set in sockets formed i , P , FIG. 24. — Number and Positions in the bone ot the upper and of Teeth of Permanent Set. lower jaws. The region of the jawbones where the teeth are imbedded is covered by the gums. 1 See "Laboratory Exercises," No. 17. 2 See "Laboratory Exercises," No. 17. 78 STUDIES IN PHYSIOLOGY Kinds of Teeth.1 — In the complete set of an adult there are thirty-two teeth. They may be divided into four groups, each kind of tooth having a definite type of structure that adapts it for a special use. In front there are eight teeth with chisel-shaped edges. The four upper teeth work upon the corresponding teeth of the lower set something like the blades of a pair of scissors ; these eight teeth have, there- fore, received the name in-cis'ors (Latin inci'sum, from inci'do, inci'dere = to cut into). Just behind the incisors on either side of the jaw is a tooth resembling the sharp-pointed teeth in the mouth of 123 4 a dog ; from this fact these four teeth in the hu- man mouth are called canines' (Latin ca'nis = dog). Still far- ther back in each half jaw are two bi-cus'- pids (Latin bi = two 4- cuspis = point), so called because the free end of each has two projections, one of which lies next the cheek, the other toward the interior of the mouth. (In other ani- mals, the teeth corresponding to the bicuspids of man are called pre-mo'lars.) The three back teeth on either side of the upper and lower jaws have broad surfaces, from which project four or five elevations. When the food is caught between these mo'lar teeth (Latin molaris = a, millstone), it is ground into a pulpy condition, and thus is well prepared for mixture with the digestive juices. Dental Formula. — For convenience in comparing the teeth of different animals we use a form of expression called a FIG. 25. — Teeth from Half of Upper Jaw. 1 = incisors. 2 = canines. 3 = bicuspids or premolars. 4 = molars. 1 Teeth of various kinds should be procured from a dentist, and should be cleaned by boiling in a solution of caustic soda. A STUDY OF BLOOD MANUFACTURE 79 dental formula. It consists of a series of fractional represen- tations, the numerators of which represent the teeth in the upper jaw, while the denominators show the corresponding teeth of the lower jaw. The incisors, canines, premolars (bicuspids), and molars are indicated by their initial letters. The dental formula of man is, therefore, 2 + 2 1 + 1 2+2 which means that the adult human being should have 8 incisors, 4 canines, 8 bicuspids, and 12 molars. Milk Teeth. — During early childhood there appears a first set of milk teeth, which later are loosened and displaced by the growth of the permanent set that we have just described. There are but twenty teeth in the milk set, and the formula is as follows : 2 + 2 1 + 1 2 + 2_ Bicuspids are therefore wanting, and the milk molars occupy the position in each half jaw which later is filled by the two bicuspids of the permanent set; hence, the molars of the per- manent set develop in a region of the jaw that bears no teeth during childhood. The teeth appear gradually, the lower incisors usually being the first to push through the gums at about the sixth month. The third permanent molars of each half jaw often appear as late as the twentieth year; they are called the wisdom teeth.1 Structure of Teeth. — The exposed portion of a tooth is called its crown. It is covered with a layer of e-nam'el, which is the hardest tissue in the body. The root or fang of 1 The roots of the milk teeth are gradually absorbed and finally the teeth loosen and come out. This process is called " shedding" and is very slow, occupying, in some cases, a year or more. The milk teeth are replaced by the permanent teeth, which appear usually after the milk teeth are shed. The following table, compiled from Bromell's 80 STUDIES IN PHYSIOLOGY the tooth is imbedded in a socket in the bone of the jaw. It has no enamel, but instead its outer layer is a modified bone tissue called cement substance. The incisors and canines usually have but a single root ; the bicuspids may have two ; and the molars are often held in the jawbone by three, four, or five fangs. In the region between the crown and the fang is the neck of the tooth, which is surrounded by the gums. The internal structure of a tooth is well shown in a verti- cal section. The covering of enamel is thickest over the top of the crown ; it becomes thinner down the exposed sides, and disappears in the neck region. The largest part of the tooth is composed of the bony den'tine, which consists of fine processes extending from the cells in the pulp cavity " Anatomy and Histology of the Mouth and Teeth," gives approxi- mately the time when these changes occur. APPEARANCE OP MILK TEETH BEGINNING OF SHEDDING PROCESS APPEARANCE OF PERMANENT TEETH Lower central incisors .... 6- 8 months 7th year 7- 8 year Upper central incisors .... 6- 8 months 7th year 7-8 year Lower lateral incisors .... 7- 9 months 8th year 8- 9 year Upper lateral incisors .... 7- 9 months 8th year 10-11 year Lower canines 17-18 months 12th year 12-13 year Upper canines .... 17—18 months 12th year 12-13 year Lower 1st deciduous molar ( = lst permanent bicuspid) 14-15 months 10th year 10-11 year Upper 1st deciduous molar . . 14-15 months 10th year 10-11 year Lower 2d deciduous molar . . 18-24 months 11-12 year 11-12 year Upper 2d deciduous molar . . 18-24 months 11-12 year 11-12 year Lower 1st permanent molar . 6- 7 year Upper 1st permanent molar . 6- 7 year Lower 2d permanent molar . 12-16 year Upper 2d permanent molar . 12-14 year Lower 3d permanent molar . Wisdom teeth 16-20 year Upper 3d permanent molar . Wisdom teeth 17-20 year A STUDY OF BLOOD MANUFACTURE 81 and of hard intercellular substance. In the central part of the tooth is the pulp cavity. This region is well supplied with nerves and blood vessels,which enter through a small Cement or crusta petrosa Alveolar periosteum or root-membrane FIG. 26. — Longitudinal Section FIG. 27. — The Mouth widely opened, of a Canine Tooth. C.p. = circumvallate papillae of tongue. F.p. = fungiform papillae of tongue. Tn = tonsil. Uv = uvula (a projection of the soft palate). V= branches to palate of fifth nerve. VIII = branches to tongue of ninth nerve. aperture at the end of the fang. The blood furnishes the teeth with new building material, and it is probable that the nerves in some way direct the processes of nutrition. 3. THE TONGUE Structure of the Tongue. — The tongue is an elongated mass of muscular tissue., attached behind to the floor of the mouth. 82 STUDIES IN PHYSIOLOGY The muscle fibers run through it in three directions, and by their separate or combined action the free end of this organ can be moved about at. will. When one examines the mucous membrane on the upper surface of the tongue, one sees elevations of different sizes, called pa-pil'lae (see p. 294). Nerve fibers carry messages from the papillae to the brain, and thus we become conscious of the senses of taste and touch. Functions of the Tongue. — The tongue has the following uses : (1) it pushes the food between the teeth and so helps in the process of mastication ; (2) it is the principal organ of taste ; (3) as soon as the food is ready to be swallowed, the tongue arches upward and forces the pasty mass back into the throat ; (4) the tongue is likewise essential in speak- ing. The so-called lingual (Latin lingua = tongue) conso- nants, t, d, and n, are pronounced when the tongue touches the roof of the mouth. 4. THE SALIVARY GLANDS Position and Action of the Salivary Glands. — In addition to the mucus given out by the mucous membrane, the mouth receives another secretion called sa-li'va. At the sight or smell of tempting food, "the mouth waters." A sudden fright or nervousness, on the other hand, stops the flow of this secretion. Saliva is secreted by the salivary glands. Two of these glands, the pa-rot'ids (Greek, meaning "beside the ear"), are located near the back part of the lower jaw- bone just beneath and in front of the ear. Any one who has had the mumps can readily locate these organs, for mumps is a disease in which the parotid glands swell. From the parotid gland of each side a duct conveys saliva along through the walls of the cheek. This duct opens at the apex of a small elevation, easily felt with the tip of one's tongue, on the inside of the cheek opposite the upper second molar teeth (Fig. 28). A STUDY OF BLOOD MANUFACTURE 83 Two other pairs of glands, the sub-max'il-la-ry (Latin sub = beneath + maxilla = jawbone), and the sub-lin'gual (Latin sub = beneath + lingua = tongue), lie in the muscu- lar floor of the mouth cavity, and the ducts from these glands open in the floor of the mouth under the tongue. Microscopic Structure of Salivary Glands. — Each of the salivary glands, when dissected and examined with the microscope, reminds one of a bunch of grapes, and for this reason this type of gland is called rac'e-mose (Latin race- mosus = full of clusters). The principal duct of the gland may be compared to the main stem of the grape cluster, and connected with this duct are the small ductules (Latin duc- tus= pipe + ulus = little) which answer to the small grape stems. At the end of the ductules are the tiny hollow spheres or gland recesses (re- sembling grapes in form), the cells of which secrete the sa- liva. All parts of the gland are surrounded and held to- gether by fibers of connective tissue. Blood vessels bring to the gland cells the raw mate- rials from which the saliva is produced. The workings of the gland are largely controlled by nerve fibers that run from the brain. In brief, then, the essential elements of the salivary glands, or of any other glands, are the special gland cells, the blood vessels, and the nerves. Uses of Saliva. — (1) The saliva aids the mucus in keeping the mouth moist, and thus we are enabled to talk easily. FIG. 28. — Dissection to show the Salivary Glands. a = sublingual gland. b = submaxillary gland, c = parotid gland. d = ducts from sublingual and sub- maxillary glands. e = duct from parotid gland. 84 STUDIES IN PHYSIOLOGY (2) It moistens the food for swallowing. The importance of this function is appreciated when one tries to hurry in swallowing the crumbs of dry cracker. (3) Saliva dissolves sugar and salt. If the tongue is wiped dry and a piece of sugar is placed upon it, we have no sensation of taste until the sugar has been partially dissolved by the mixture of saliva and mucus which are poured upon it. (4) Besides the three mechanical functions of saliva that we have just enumerated, this secretion has a chemical action upon cooked starch.1 After a bit of tasteless starch paste has remained on the tongue for a short time, we notice that it becomes sweet. This means that the starch has been changed to grape sugar by the saliva. Following is a still better method of demonstrating the character of this change. Put a bit of the starch paste into a test tube and mix with it some saliva from the mouth. After warming the mixture, pour in some Fehling's solution and boil. The deep orange or red color clearly demonstrates the presence of grape sugar. Since neither starch nor saliva gives the slightest test with the Fehling's solution, the grape sugar must have resulted from the chemical action of the saliva on the starch. The principal ingredients of saliva are water (constituting over 99% of its composition), and a kind of digestive ferment called pty'arlm (Greek ptyalon — spittle). It is the ptyalin that changes the starch to grape sugar. 5. THE THROAT CAVITY The Uvula. — The mouth cavity communicates with the throat by a somewhat narrow opening. If one holds a mir- ror in front of the mouth opening and presses down upon the tongue with a spoon, one sees hanging down a small fingerlike extension of the soft palate, called the u'vu-la. When food is swallowed, this little tongue of the soft palate is shoved backward into a horizontal position, where it iSee "Laboratory Exercises," No. 19. A STUDY OF BLOOD MANUFACTURE 85 helps to separate the lower part of the throat cavity from the upper parts that commu- nicate with the nose cavity. The Air Passages and the Epiglottis. — The cavity of the throat is more or less conical in shape, the apex of the cone narrowing below into the esophagus. The windpipe (tra'chea) lies in front of (or ventral to) the gullet and conducts the air from the throat cavity to the lungs. At the top of the windpipe is the voice box (lar'ynx). This is readily felt on the ventral surface of the neck and is com- monly known as "Adam's apple." When the food is being swallowed, it is of course important that the windpipe be closed, and this is. accomplished by a little trapdoor called the ep-i-glot'- tis (Greek epi= upon -{-glottis = opening from the throat into the larynx). If one puts one's finger on the larynx region and then swal- lows, one can feel this organ rising to meet the epiglottis. Breathing and Swallowing. — Thus far we have de- scribed five openings con- nected with the throat cavity : two for the food (one lead FIG. 29.— Longitudinal Section of Head and Neck, showing Food and Air Passages. a = vertebral column. 6 = esophagus, c = windpipe. d = larynx. e = epiglottis. / = soft palate and uvula. g = opening of left Eustachian tube. h = opening of left tear duct. i = hyoid bone. k — tongue. I = hard palate. m, n = base of skull. °>P>Q = upper, middle, and lower turbinate bones. 86 STUDIES IN PHYSIOLOGY ing from the mouth, the other opening into the gullet), and three for the air (the first two letting in the air from the nose, the third, conducting it through the glottis) to the lungs. But one set of these openings can be used at the same time, for one sees from Fig. 29 that the paths of food and air cross each other in the throat. Hence, if we try to breathe and swallow at the same instant, the food starts " down the wrong way," that is, down the windpipe. The Eustachian Tubes. — A simple experiment demon- strates the presence of an additional pair of openings, con- necting the throat with the ear. Close the mouth, grasp the nose firmly so as to close its external openings, and then force air upwards several times from the lungs. The crack- ling sound is due to the momentary stretching of the ear drums by the increased pressure of the air on their inner surface. The Eu-sta'chi-an tubes (so named from their dis- coverer, a learned Italian physician), carry this air from the upper part of the throat cavity into the middle region of the ear. The ringing sensation in the ears when one has a cold in the head is due to the temporary closing of these tubes. The Process of Swallowing. — The food can be kept in the mouth as long as we wish, but when once it has been pushed back into the throat it is beyond our control. The uvula blocks the way toward the nose cavity, the windpipe is closed by the epiglottis, and the muscles that surround the throat cavity quickly close in about the food and force it down the gullet. This rapid clearing of the throat is nec- essary in order that breathing may be resumed. As soon as the food reaches the gullet, the windpipe is opened by the lowering of the larynx and by the elevation of the epiglot- tis, and at the same time the soft palate drops down into a vertical position, thus opening the passages from the nose. Hence, when food particles start down the windpipe and we cough, the food is often forced out through the nose, since this is the only passage way that is clear (see Fig. 29). A STUDY OF BLOOD MANUFACTURE 87 6. THE ESOPHAGUS Structure of the Esophagus. — The esophagus traverses the length of the chest cavity, and as it nears the stomach it goes through the diaphragm. In a cross section of this tube the following tissues appear. Like all other parts of the alimentary canal, it is lined with mucous membrane, which furnishes a soft, moist surface for the passage of food. Outside the mu- cous membrane are rings of circular muscle running around the esopha- gus, and a longi- tudinal layer of muscle is found outside the circu- lar muscles. Functions of the Esophagus. — The food is pushed slowly down this « = esophagus. 6 = cardiac region of stomach. c = upper wall of stomach. d = pyloric region of stomach. e — bile duct from liver. /= gall bladder. g = duct from pancreas. h, i = small intestine showing ridges. FIG. 30. — Longitudinal Section of Stomach and Small Intestine. straight tube by the successive contrac- tion of the rings of muscle described above. Swallowing is, therefore, not a mere dropping of the food into the stomach, for the walls of the esophagus are pressed together by surrounding organs, except when the tube is opened by the passing food. In fact, after practice one can swallow when standing on one's head, and most quadrupeds (horse, dog, cow) when feeding hold the head below the level of the stomach. 88 STUDIES IN PHYSIOLOG1 7. THE STOMACH Position, Size, Shape. — The stomach lies about midway between the upper and lower ends of the trunk, with its larger end lying toward the left side of the body. It is a muscular pouch, shaped more or less like a pear or a crook- neck squash. When moder- ately filled, it holds about three pints. The esophagus communicates with the upper region of the larger end of the stomach, and since this opening into the stomach is near the apex 'of the heart, c it has received the name car'- di-ac orifice (Greek Tcardia = heart). The small intestine is continuous with the right end of this organ, the com- munication between the two the py-lo*rus (from Greek, gate keeper) being by a ring of muscle 'ic sphinc'ter FIG. 31. -Three Gastric Glands (Cardiac Portion of Stomach). = connective tissue between called the (from Greek, meaning to bind tight) (see Pig. 30). The Mucous Lining and Gastric Glands. — When the stomach is full of food, the lining pre- sents a smooth surface. This becomes folded into ridges as the food is forced outward into the intestines. The important glands of the stomach are those which secrete the gas'tric juice. This digestive fluid is composed of water (over 99%), free hy-dro-chlo'ric acid, glands. e = cells lining the stomach, ra = mouth of gland. ov = ovoid cells (possibly secrete hydrochloric acid). p = cylindrical cells (probably se- crete pepsin) . A STUDY OF BLOOD MANUFACTURE 89 and a digestive ferment called pep 'sin.1 If one examines with a magnifying lens the mucous lining of the stomach, one sees a countless number of small orifices that look like pinholes. These are the pores through which gastric juice is dis- charged from the gas'tric glands. The microscopic structure of one of these glands is best studied in a thin section cut at right angles to the surface through the wall near the car- diac end of the stomach. The surface pore is the opening from a compara- tively short duct, and connected with this are two or three tiny finger- shaped recesses, each one of which is lined with a single layer of cy- lindrical cells (Fig. 31). Outside this layer are other egg- shaped cells, which give to the gas- tric glands their peculiar beaded ap- pearance. It is probable that the pepsin of the gastric juice is secreted by the cylindrical cells. It is then discharged through the ducts when the food enters the stomach. The origin of the hydrochloric acid has never been satisfactorily explained; some physiologists believe, how- ever, that it comes from the egg-shaped cells mentioned above. Blood Supply of the Stomach. — Beneath the mucous lining of the stomach is a rich supply of blood vessels. The blood brings to the stomach the chemical compounds necessary for 1 In the gastric juice is also found another ferment called ren'nin, which coagulates milk. Mucous lining containing glands. Submucous layer contain- ing blood ves- sels and con- nective tissue. Circular, ob- lique, and 1 i gitudinal muscles. Outer covering of connective tissue. FIG. 32. — Section of Wall of Stomach. Magnified twelve times. Photographed through the microscope. 90 STUDIES IN PHYSIOLOGY the secretion of gastric juice, supplies the building materials required for the growth and repair of the muscles, and, as we shall see later, carries away from this organ whatever digested food it can absorb. Muscles of the Stomach. — The chief function of the human stomach is to secrete the gastric juice and to mix thoroughly this juice with the food. The muscular walls are admirably adapted to this purpose. On stripping off the outer cover- ing of connective tissue, one finds layers of longitudinal, circular, and oblique muscles that constitute the larger por- tion of the thickness of the stomach wall (Fig. 32). Cir- cular fibers form the strong ring of muscle (pyloric sphincter) that closes the pyloric end of the stomach from the small intestine (Fig. 31, d). When the food reaches the stomach, the gastric juice oozes out upon it, and the mixture is pushed back and forth and up and down by the successive action of the different sets of muscles. The return of the food to the mouth cavity is prevented by the contraction of the circular muscles at the cardiac orifice, except in case of nausea, when they relax and allow the stomach to rid itself of its contents. The pyloric sphincter relaxes from time to time, and the food that has been sufficiently digested is pushed on into the intestine. Fortunately for the well-being of the body, all these processes are entirely automatic, that is, they are carried on without our conscious direction. The muscles of the alimentary canal for this reason are called in-voVun- ta-ry (Latin in = without -f voluntas = will). Their activ- ity is largely controlled by the syni-pa-thet'ic nervous system, which will be described later. Digestion in the Stomach.1 — The gastric juice has no effect whatever on the nutrients starch and fats. Sugars and soluble salts (that is salts that dissolve in water), if not dissolved in the mouth, are readily liquefied by the water of the gastric juice. i See "Laboratory Exercises," No. 20. A STUDY OF BLOOD MANUFACTURE 91 Certain mineral food substances, however, like phosphate of lime found in milk, are not soluble in water, and these insoluble salts reach the stomach unchanged. The hydro- chloric acid of the gastric juice soon converts them into soluble salts, which are then dissolved. Thq, following ex- periment will illustrate this process. Put a little of the phosphate of lime into a test tube, add water, and shake. The mixture assumes a milky appearance, and after a time the phosphate of lime settles to the bottom, showing that this kind of mineral matter will not dissolve in water. The addition of a small amount of hydrochloric acid immediately clears the mixture, for the phosphate of lime is converted into chloride of lime, which is a soluble salt. Digestion of Proteids.1 — The most important function of the stomach is its digestive action on proteids. The white of egg, lean meat, or the gluten of wheat reaches the stomach in a pulpy mass, and this is insoluble in water. The casein of milk, which is a liquid when swallowed, becomes curdled by the action of the hydrochloric acid. Before these most important proteids can be absorbed to become a part of the blood, they must be chemically changed into a kind of soluble proteid called pep'tone. The principles of proteid digestion can be illustrated in the following way : Cut into fine bits a piece of hard-boiled egg, and divide the minced egg into four portions. Put one fourth into a test tube (No. 1) and add water. Into another test tube (No. 2) put a second portion of minced egg, water, and a little hydrochloric acid. To a third portion (test tube No. 3) add water and a little pepsin. (Pepsin readily dissolves in water.) The rest of the egg in test tube No. 4 should be treated with all the in- gredients of gastric juice (water, pepsin, and hydrochloric acid). Since the food in the stomach is in constant motion, and since the temperature within the body (98 i° F.) is considerably higher than that of the surrounding air, these conditions should be imitated so far as possible by frequently 1 See "Laboratory Exercises," No. 21. 92 STUDIES IN PHYSIOLOGY shaking the tubes and by leaving them in a warm place. At the end of several hours, the egg in test tube No. 4, which was treated with all the ingredients of gastric juice, is found to be dissolved, but the pieces remain practically unchanged in ^Jie other tubes. We infer therefore that the proteid of egg is digested by the combined action of pepsin, hydrochloric acid, and water. An instructive experiment may be performed in a fifth test tube by adding the three ingredients of gastric juice to a large piece of egg. It will be found that a much longer time is required to digest the egg in this condition. Hence, we see that if food is not properly chewed, the stomach is compelled to ck) a considerable amount of extra work. One might ask the interesting question, Why does not the stomach digest itself ? When we eat a piece of tripe, which is prepared from the walls of a cow's stomach, the tripe is liquefied by our gastric juice. Why, then, does not our gastric juice dissolve the walls of our stomach? All we know is that in some unknown way our stomach tissues when alive are able to resist this solvent action. 8. THE SMALL INTESTINE Position and Size. — The small intestine is a much coiled tube, filling the larger portion of the abdominal cavity (see Fig. 23). It is usually twenty feet or more in length, and therefore constitutes nearly four fifths of the whole length of the alimentary canal. Beginning at the pyloric end of the stomach with a diameter of about two inche^ it decreases somewhat in size until it opens into the large intestine. Peritoneum. — The whole abdominal cavity is lined with a thin, smooth membrane called per-i-to-ne'um (Greek peri = around -f- teinein = to extend). Sheets of peritoneum like- wise inclose the various organs found in the abdominal cavity, and connect these organs with the wall of the ab- domen. Per-i-to-ni'tis is an inflammation of any portion of this membrane. To the thin sheets of connective tissue and A STUDY OF BLOOD MANUFACTURE 93 peritoneum that hold the small intestine, in place is given the name mes'en-ter-y (see Fig. 33). Functions of the Small Intestine. — In order to understand the structure of this part of our digestive organs, we must bear in mind that one of its principal functions is to soak up or absorb digested food. To accomplish this, the food must be moved along slowly close to the minute blood vessels and other tubes which are to carry off to other parts of the body FIG. 33. — Diagram of Cross Section of Abdomen. (In reality the larger part of the abdominal cavity is filled with the coils of the intestine.) b.v = blood vessels. d.m = muscles of the back. m1, m2, m8 = three muscle layers of abdominal wall. rues = mesentery. perit = peritoneum. sk = skin. vert = vertebra. the liquefied nutrients. We shall soon see the wonderful adaptations of the intestine for this purpose. In the intestines, too, important digestive processes are carried on by the juices that come from the liver and pan- creas. The chemical changes in the food brought about by pancreatic juice and bile will be discussed in connection with the organs by which these digestive fluids are secreted. Beneath the peritoneum are layers of circular and longitu- dinal muscle. By their rhythmical contraction the food is 94 STUDIES IN PHYSIOLOGY slowly forced on toward the large intestine. This succession of contractions and relaxations is called per-i-stal 'sis. Adaptations for Absorption. — In the small intestine the mucous membrane is developed to an extraordinary degree. In the first place this lining is elevated into ridges that run two thirds of the way around the interior wall and some of them project about a third of an inch into the cavity of the FIG. 34. — Cross Section of Intestine of a Mouse. (Ridges are not present.) Magnified fifteen times. Photographed through the microscope. A large number of villi project toward the interior of the intestines. The dark lines show the blood vessels filled with a colored mixture. intestines. These crescent-shaped ridges are most numer- ous near the stomach and gradually disappear in the region near the large intestine (Fig. 30). Like little dams, they delay the onward flow of the food, and they also increase considerably the surface for absorption. The absorbing surface is multiplied still further by the vil'li. The Villi. — If one puts into water a piece of the small intestine of a sheep, and examines with a hand lens the mucous lining, one sees that the ridges and depressions are A STUDY OF BLOOD MANUFACTURE 95 covered with tiny hairlike processes that give a velvety appearance to the surface. Each of these minute elevations is called a vil'lus (Latin vittus = a tuft of hair). The villi are exceedingly numerous in the small intestine of man, the total number being estimated at about four millions. Each villus, when highly magnified, is found to be a com- plicated structure. Up through its center pass one or more hollow tubes, the closed ends of which lie just beneath the cells that cover the top of the villus. The tubes of the different villi connect with one another and are of great importance in carrying away from the intestine the fats that are absorbed. If a cat is fed with milk and after three or four hours is killed, one can see that these minute vessels in the villi and the larger tubes in the mesentery into which they empty are filled with a milky stream of the absorbed fat droplets. For this reason the tubes are called lac'teals (Latin lac, foc&'s = milk). Around the lacteal of each villus is a network of minute blood vessels. Since they lie close to the single layer of cylindrical cells which cover the outer surface of the villus, the liquefied food is readily absorbed by the blood current. One may therefore compare the absorbent action of the villi with the absorption that takes place through the walls of the root hairs of plants. In structure, however, a villus is very much more complicated than is a root hair. FIG. 35. — Diagram of Two Villi, highly magnified. b.v = blood vessels. e = cells covering villi. I = lacteals for absorbing fat. 96 STUDIES IN PHYSIOLOGY 9. THE LARGE INTESTINE Position, Form, Size. — The large intestine is the last por- tion of the alimentary canal. It is a tube 'five or six feet long, with a diameter gradually decreasing from two and a half or three inches to an inch at its lower end. Beginning in the lower right-hand region of the abdominal cavity as a saclike pouch called the cm' cum (Latin caecum = blind sac) (Fig. 23), the large intestine passes anteriorly on the right side (the ascending colon) to the lower surface of the stom- ach ; it then crosses the abdominal cavity (transverse colon) ; a third portion (the descending colon) runs posteriorly on the left side. The large intestine then takes an S-shaped course (sigmoid flexure) and passes to the exterior of the body by a short, straight tube, the rectum (Latin rectus = straight). Ileo-caecal Valve. — The final portion of the small intestine (called the il'e-um) opens into the side of the large intestine in the region of the caecum by a so-called il-eo-cce'cal orifice. This is guarded by two flaps of membrane. The food can pass into the large intestine, but its return to the small in- testine is prevented by this double-flapped ileo-ccecal valve, which works on the same principle as the valve in a bicycle tire; after air has been forced into the tire, the valve immediately closes to prevent its escape. Vermiform Appendix. — Connected with the caecum is a small tubelike sac about the size of a pencil, and usually about four inches long (Fig. 23). From its more or less twisted shape it has received the name ver'mi-form ap-pen'dix (Latin vermiform = worm-shaped). The appendix of rab- bits (see Fig. 4, P) and of several other herbivorous animals is of considerable use in the process of absorption. In man, however, it has lost this importance, and remains as a small and probably useless extension of the caecum. Ap-pend-i- ci'tis is a diseased condition arising from inflammation in the tissues of the appendix.. A STUDY OF BLOOD MANUFACTURE 97 10. THE PANCREAS Position, Form, Size. — One of the most important of the digestive glands is the pan'cre-as, which is situated just below the stomach. In shape this organ may be compared with that of a dog's tongue. It extends horizontally from a curve of the small intestine near the pylorus to the spleen at the left side of the body (Fig. 23). The pancreas is usu- ally a little over six inches in length. Structure of the Pancreas. — Like the salivary glands, the pancreas is a racemose gland, consisting of gland recesses, ductules, and a main duct. The latter extends through the length of the pancreas, and after uniting with a duct from the liver (Fig. 30, g), opens into the small intestine not far from the pylorus. Within the gland recesses is secreted the pancreatic juice, which is poured out through the duct just described upon the food after it has entered the small intestine. Functions of the Pancreatic Juice. — The pancreatic juice is alkaline. The food mass, therefore, becomes alkaline soon after it enters the intestine. Pancreatic juice digests three of the nutrients, namely, starch, proteids, and fats. Indeed, with the single exception of insoluble salts, our foods could be digested by this one juice. Like saliva, pancreatic juice changes starch into sugar, and like gastric juice, it converts proteids into peptones. The pepsin of the gastric juice, however, always requires the presence of an acid (hydro- chloric), while the ferments of the pancreatic juice work only in the presence of an alkali. Digestion of Fats.1 — The heat of the body melts much of the fat before it reaches the intestine, but this liquid cannot be absorbed until it has been digested more thoroughly. Pancreatic juice digests fats in two ways : either by making them into an e-mul'sion, or by converting them into soap and glycerin. The latter process is called sa-pon-i-Ji-ca'tion (Latin sapo = soap -\-facere = to make). These changes are shown 1 See "Laboratory Exercises," No. 22. H 98 STUDIES IN PHYSIOLOGY in the following experiments : Put into a test tube a small amount of olive oil or melted butter, add water and shake. The oil is broken up into small spheres and mingled with the water during the process of shaking. When the test tube is set aside, however, the oil rises to the surface, show- ing that the two liquids will not remain combined. If, now, a solution of caustic, soda or other alkali be shaken up with the oil and water, the mixture assumes a milky appearance, and the oil does not then rise to the top in a clear layer as it did after being shaken with the water. Fat, when thus mixed with an alkali, forms an emulsion. If a drop of this mixture is examined with a compound microscope, tiny spheres of fat are seen floating about in a colorless liquid. Each little sphere is inclosed by a thin covering of the alkali, and thus the fat droplets are kept separate from each other. Water will not form this thin covering, nor will an acid. For this reason, fats are not emulsified in the stomach. They are acted upon only by the strongly alkaline juices of the intestine. A still better emulsion can be formed by shaking the oil with raw white of egg. In this case the fat globules are surrounded by a thin layer of albumin. Milk is an emulsion consisting of fat (cream) and of liquid proteids. When the emulsion, made by mixing the oil and the alkali, is heated, a chemical change takes place and some of the fat is converted into soap and glycerin. Both of the latter are readily soluble in water, and so can be easily taken up by the blood. The pancreatic juice acts upon fats in both the ways we have been describing. Since it is alkaline, it forms an emulsion. It can likewise change fats into soap and glycerin. When these compounds get into the blood, however, they are changed again into fats. 11. THE LIVER Position, Form, Size The human liver is the largest gland of the body, weighing three to four pounds. It lies toward A STUDY OF BLOOD MANUFACTURE 99 the right side of the body, just beneath the diaphragm, and partially covers the py- loric end of the stomach. It consists of several lobes, and on its under surface is a small, green- ish brown sac called the gall bladder. The deep red color of the liver is partly due to the fact that one fourth of all the blood of the body is found within its tissues. Functions of the Liver. — The liver performs three important func- tions. In the first place, it secretes a golden brown liquid called the bile, which is either poured at once through the bile duct into the small intestine or is stored in the gall blad- der until needed. If the bile duct becomes stopped up, the bile is absorbed into the blood and gives to the tissues the yellow tint that is characteristic of jaun- dice. The liver, in the second place, serves as a great storehouse for the carbohydrates when the blood does not need them for immediate use. FIG. 36. — The Organs of the Abdomen. ac = ascending colon (cut off at top). ad = descending colon (cut off at top). a, b, c,d,e = portal vein and its branches which carries blood to liver from stomach, spleen, pan- creas, and intestines. du = part of small intestine (cut off). gT) = gall bladder. . h = ducts from gall bladder and liver. I = under surface of liver. p = pancreas. sp = spleen. st = stomach. We shall see 100 STUDIES IN PHYSIOLOGY in a later chapter that all the blood from the stomach and intestines passes through the liver on its way back to the heart. If this blood contains more sugar than is needed, the excess is left behind in the liver cells, where it is changed to a kind of animal starch called gly'co-gen. When, on the other hand, there is a lack of carbohydrates in the blood, some of the supply in the liver is changed back to sugar and is taken up again by the blood. Finally, the liver helps to destroy some of the worn-out cells of the blood (the red corpuscles), and the waste materials thus formed are passed off into the intestine as a part of the bile. Functions of the Bile. — We have already noted the fact that the bile duct and the duct from the pancreas unite before reaching the intestine. Hence, the bile and pancreatic juice are mixed when they are poured upon the food. It is difficult, for this reason, to distinguish with certainty between the functions of the two juices. Some physiologists main- tain that the bile forms an emulsion with fats after the same manner as the pancreatic juice; others declare that it has no digestive action whatever, and is merely a waste ma- terial passed off by the liver into the intestine. We know that the bile is alkaline; it is therefore probable that at least it assists the pancreatic juice in digesting fats. It is certainly true that the absorption of fats through the cells of the villi into the lacteals is promoted by the presence of bile, for in cases of jaundice a considerable percentage of the fats we eat is discharged from the large intestine with the waste material. Again, the alkaline bile causes the muscles of the intestines to contract rhythmically, thus forcing the food onward toward the large intestine. For this reason, the best means of avoiding constipation is to secure the presence of a sufficient quantity of bile in the intestine. Calomel and similar drugs are often given in case of constipation, because they stimulate the liver to greater activity. And, finally, bile acts as an antiseptic to prevent the decay of the refuse material as long as it remains within the intestines. A STUDY OF BLOOD 12. ABSORPTION FROM THE ALIMENTARY CANAL Necessity for Absorption. — We have now learned some- thing of the processes of digestion. We have seen that the foods we eat are ground up in the mouth cavity by the teeth, and thus made ready for the action of the various digestive juices. We have also demonstrated that sugars and soluble salts are dissolved in the mouth ; that insoluble mineral matters are made soluble in the stomach; that starch is changed to sugar by the saliva and pancreatic juice ; that proteids are converted into peptones by the pancreatic and gastric juices ; and that fats are emulsified or saponified in the intestines by the combined action of bile and pan- creatic juice. Were the food to remain within the alimentary canal, however, even though it had been thoroughly digested, it would still be, in a certain sense, outside the body, since this canal is a continuous tube opening to the exterior at either end. In order to furnish material for building and repairing the various tissues, the liquid nutrients must be distributed to the tissues, wherever needed. This is accom- plished through the agency of the blood system. We have now to consider the process of absorption, which includes the final steps whereby foods become a part of blood. By absorp- tion is meant the passage of the digested food through the lining of the alimentary canal, and through the thin walls of the count- less blood vessels and lacteals that lie close at hand. To under- stand this process we must first consider — The Principles of Osmosis.1 — An apparatus for the demon- stration of osmosis is shown in Fig. 37. Over the larger end of a thistle tube is tied a piece of the intestine of a sheep or pig. The tube is half filled with a thick solution of grape sugar (honey will do as well), and is inserted in a bottle filled with water to the level of the grape sugar. The height of the thistle tube is increased by attaching a glass tube. At the beginning of the experiment we have two liquids (water 1 See "Laboratory Exercises," No. 23. idi STUDIES IN PHYSIOLOGY and grape sugar solution) of different density (the liquid within the thistle tube being the more dense), these liquids separated by an animal membrane. On examining the apparatus after several hours, we find that the solution within the thistle tube has risen several inches, while the water in the bottle is at a lower level than it was at first. It is evident that some of the water has passed through the membrane of the intestine, and has mingled with the grape sugar solution. Another fact becomes evi- dent when we boil with Fehling's solution a little liquid in the bottle outside the thistle tube. The deep red color of the mix- ture proves the presence of grape sugar. Two cur- rents, therefore, have been passing through the ani- mal membrane, but from |P the level of the two liquids we know that the amount of water that has gone into FIG. 37. — Apparatus to illustrate the ., . , . ., . , Principles of Osmosis. the thistle tube is greater than the amount of grape sugar solution that has passed out. If the apparatus is allowed to stand for several days, the liquid within the tube may rise to a height of several feet. From the preceding observations we derive the following — Law of Osmosis. — When two liquids of different density are separated by an animal (or plant} membrane, they tend to mingle, and the greater Jloiv is always from the less dense to the more dense. Two other pieces of apparatus similar to that already described should be prepared, the second thistle tube being filled with a rather thin starch paste, and the third with THISTLE TUBE THISTLE TUBE No. 1 No. 2 THISTLE TUBE NO. 3 A STUDY OF BLOOD MANUFACTURE 103 raw white of egg mixed with water. At the end of several days the liquids in both thistle tubes will be found some- what higher than the level of the water outside, showing that the denser starch paste and proteid mixtures have absorbed some water. But when we test the water outside the starch by adding iodine, we fail to find a trace of starch ; and on adding nitric acid and ammonia to the water in the second experiment, we demonstrate that little or none of the proteid has passed through the intestine. We have found, then, that some substances pass readily through an animal membrane while others do not. To the former class is given the name crys'tal-loids because many of these substances have a crystalline form. As examples of crystalloids we may mention sugar, salt, water (crystalline when frozen), and peptones (without crystalline form). Col'loids (Greek = gluelike), on the other hand, include proteids, starch, and gum, which do not readily soak through an inclosing membrane. Application of the Principles of Osmosis to Absorption. — We can now readily see the necessity for the change of starch into sugar, and of proteids into peptones, and for the emul- sion or saponification of fats. Unless these nutrients are converted from colloids into crystalloids, they cannot pass through the membranes that separate them from the blood. Although absorption cannot be wholly explained by applying the principles of osmosis, yet this is undoubtedly one of the most important factors in the process. The most favorable conditions for rapid absorption are these : (1) a considerable extent of moist, absorbing mem- brane, (2) a rich supply of blood and lymph vessels beneath this membrane, and (3) the digested food must remain for some time in close contact with the absorbing surface. Keeping in mind these requirements, let us consider the opportunities for absorption offered in each region of the alimentary canal. Absorption in the Mouth, Throat, and Gullet. — While the 104 STUDIES IN PHYSIOLOGY mouth, throat, and gullet all have a moist surface generously supplied with blood vessels, the food does not lie next the mucous membrane for any considerable time, and therefore the amount of absorption in these regions is not great. If one eats slowly, some of the dissolved salts and sugars and water are probably absorbed before reaching the stomach. Absorption in the Stomach. — In the stomach the food usu- ally remains for several hours, and one would therefore expect that a good deal of absorption would take place during this time. But we must remember that the contraction of the gastric muscles keeps the food in constant motion. This movement, while favorable for digestion, diminishes absorp- tion, because the liquefied food does not remain long enough in one place to soak into the blood. Absorption in the Small Intestine. — We therefore find that most of our food passes out of the stomach before it is absorbed. In the structure of the small intestine, however, we seem to find every possible provision for gathering up the nutrients. The amount of surface is greatly increased by the crescent-shaped ridges, and still more by the villi, thousands of which project from every square inch of the mucous lining. As the souplike food mass is pushed slowly along through the small intestine, it becomes less and less in bulk, and more and more solid, owing to the fact that the dissolved salts, sugars, peptones, and fats are largely taken up by the blood vessels and lacteals within the villi. Absorption in the Large Intestine. — The amount of absorp- tion in the large intestine is considerably less, of course, for both villi and crescentic ridges are wanting. Yet even here considerable absorption takes place. When the mass in the intestine reaches the rectum, it consists of little but the indigestible cellulose of vegetable foods, some undigested connective tissue, waste substances from the bile, the solids in the mucous secretion, and some raw starch and fats if large quantities of these nutrients have been eaten. This refuse of the food is thrown off from the body. A STUDY OF BLOOD MANUFACTURE 105 13. SYNOPSIS OF DIGESTION EEGION OF ALI- MENTARY CANAL KIND OF SECRETION PRESENT PROCESSES CARRIED ON Mouth cavity. Saliva and mucus. Mastication of food. Starch changed to sugar. Sugar and salt dissolved. Tasting of food substances. Small amount of absorption of water, salt, sugar. Throat cavity. Mucus. Passage of food and air. Esophagus. Mucus. Passage of food to the stomach. Stomach. Gastric juice, con- sisting of water, pepsin, and hy- drochloric acid, and mucus. Churning of food by the muscles. Proteids changed to peptones. Insoluble salts changed to soluble. Small amount of absorption of water, salts, sugars, peptones. Small intes- tine. Pancreatic juice, bile, intestinal juices, and mucus. Fats changed to emulsion and to soap and glycerin. Starch changed to sugar. Proteids changed to peptones. Large amount of absorption of fats by lacteals of villi. Large amount of absorption of water, salt, sugar, peptones, by blood vessels of villi. Large intes- tine. Mucus, and in- testinal juices. Small amount of absorption of nutrients. Removal of refuse of food from the body. 106 STUDIES IN PHYSIOLOGY 14. THE HYGIENE OF DIGESTION Importance of Subject. — "I have come to the conclusion/' says Sir Henry Thompson, a noted English physician, " that more than half the disease which embitters the middle and latter part of life is due to avoidable errors in diet, . . . and that more mischief in the form of actual disease, of impaired vigor, and of shortened life accrues to civilized man ... in England and throughout central Europe from erroneous habits of eating than from the habitual use of alcoholic drink, con- siderable as I know that evil to be." This statement may not be literally true of conditions here in America, but it should at least call our attention to the great importance of the hygiene of digestion. Dyspepsia in its many differ- ent forms, typhoid fever, jaundice, gout, not to mention the more common disorders of colic, cholera morbus, and con- stipation, are but a few of the ills afflicting mankind, all of which might be avoided by eating proper food in a proper manner. Hygienic Habits of Eating. — One should form the habit, in the first place, of eating slowly and of thoroughly masticat- ing each mouthful of food. The great English statesman Gladstone, who retained his vigor in old age to a remark- able degree, is said to have had the habit of biting each mouthful of food thirty-two times ; for in this way, he said, he gave each tooth a chance to work upon it. If one fol- lowed such a rule, the stomach and other organs of diges- tion would be relieved of work which they are not fitted to perform, and thus one would doubtless escape many an attack of indigestion. The process of chewing likewise stimulates the flow of saliva. Saliva not only helps digest food in the mouth, but this juice also, when swallowed with the food, incites the gastric glands to greater activity. At least a half hour should be devoted to the eating of dinner and fifteen to twenty minutes to breakfast and lunch or supper. The A STUDY OF BLOOD MANUFACTURE 107 proper digestion of food depends in no small degree upon one's mental state ; worry and disagreeable topics should, therefore, be forgotten so far as possible while one is eating, and the mealtime should be made a season of enjoyment. Regular hours of eating are of great importance, for noth- ing more commonly deranges the digestive system than the continual nibbling of food or sweetmeats between meals. One should refrain from vigorous exercise or mental exertion for a half hour or more after eating ; the reason for this will be clear after a study of the blood system. Care of the Teeth. — Too mugh stress cannot be laid on the importance of caring for the teeth, since decaying teeth are frequently painful, they are always unsightly and are usually the cause of an ill-smelling breath, and they often lead to other derangements of the alimentary canal. Immediately after eating one should brush the teeth thor- oughly on all sides, using warm water and a little castile soap or an alkaline tooth powder, and should make sure that bits of food are not left to decay between the teeth. The frequent use of dental floss or silk to clean the spaces between the teeth is essential. Pins, knifeblades, or other metallic implements, however, should never be used for this purpose. In the process of decomposition to which we have referred, acids are formed that eat away enamel and den- tine, and a cavity when once begun grows rapidly unless the decay is stopped. For this reason alkaline tooth powders are recommended to counteract the possible effects of acids. A dentist should be consulted at least once a year, in order that the " tartar " may be removed and the cavities filled while they are small. The teeth ought never to be used to crack nuts or to pull out nails, for while the enamel is a very hard substance, it is also brittle and can be cracked or broken off by such treatment ; if once lost it will not grow again. Adaptation of Foods to Individual Needs. — The growing child should be supplied with a simple diet composed of milk, cereals, eggs, bread, and fruits, and parents should exercise 108 STUDIES IN PHYSIOLOGY great care to prevent boys and girls from eating indiges- tible compounds. It is of course impossible in a few words to give anything like a complete account of the rela- tion of food to the needs of various individuals. One person finds, for instance, that for some reason he cannot eat straw- berries or cucumbers. Since these foods act like a poison in his system, they must of course be avoided. The regula- tion of diet in time of sickness is a most important aid to recovery. In certain diseases it is necessary that some kinds of food should be forbidden, Whenever the functions of the body are not carried pn with their accustomed vigor, the physician prescribes foods that are easily digested, — for example, milk, raw oysters, toasted bread, and soft-boiled eggs. Prevention of Constipation. — Constipation, or the stoppage of the refuse of the food in the intestine, is one of the most frequent causes of discomfort, and to insure a state of health the useless residue should be expelled from the large in- testine regularly each day. Constipation may usually be counteracted by liberal drinking of water, especially a half hour before breakfast, and by eating foods with laxative effect, — for example, ripe fruits (especially figs), green vegetables, and breads made of the coarser graham and rye flours. The Use of Patent Medicines. — The enormous sale of patent medicines, soothing sirups, and " pain killers " in our country is a source of incalculable harm. It is easy enough for the makers of these nostrums to describe the symptoms of the disease which the medicine is warranted to cure, and so create a greater demand for it. Too often, as we have seen (p. 39), these compounds contain alcohol, morphine, or other dangerous ingredients. They should never be given, however highly recommended, without the advice of a com- petent physician. When an attack of sickness does not readily yield to a treatment of diet and rest, it is always safer and more economical in the end to consult the family A STUDY OF BLOOD MANUFACTURE 109 physician and, what is of equal importance, to follow his directions implicitly. Effects of Alcoholic Drinks on the Organs of Digestion. — Alco- hol, unlike most of the substances taken into the alimentary canal, requires no digestion. It can, therefore, be absorbed very rapidly by the blood, and hence alcohol is probably sometimes of great value when administered by physicians, in cases when ordinary food cannot be digested. In health, however, alcoholic drinks must be regarded as an expensive and extremely dangerous source of energy. According to the best authorities, small quantities of alcohol (when sufficiently diluted) seem for an adult to stimulate an increased flow of saliva and gastric juice. The time required for the digestion of food, when alcohol is present, in these small quantities, does not seem to be increased. Entirely different effects follow, however, when strong distilled liquors are taken, and alcohol in any large quantity often produces serious disturbances of the organs of digestion. This is especially true when liquors are taken without food, that is, between meals. The constant danger that the moderate use of beer and the light wines will lead to an uncontrollable thirst for alcohol cannot be emphasized too strongly. All authorities agree, too, that the growing youth should let alcohol entirely alone. 15. A COMPARATIVE STUDY OF DIGESTION A Study of Teeth. — Among the various groups of inverte- brates, one finds structures that have a function more or less like that of teeth. Beetles and grasshoppers, for ex- ample, have two horny jaws that move from side to side, which they use to bite their food. In the mouth of the lobster and crayfish similar structures are found, and in addition these animals have strong teeth in the stomach that grind against one another. This arrangement is called a, "gastric mill." Many snails have a great number of mi- 110 STUDIES IN PHYSIOLOGY nute teeth upon the tongue. In obtaining their food the;y use this rough movable tongue like a file. Among the vertebrates teeth are wanting in all birds, in toads, turtles, and tortoises. Most of these animals, how- ever, have horny beaks that aid them in crushing their food. Frogs have teeth along the upper jaw and on the roof of the mouth (see Fig. 83) ; these teeth are used prin- cipally to prevent their prey from escaping and to aid in swallowing. In rattlesnakes and other venomous reptiles two or more long, sharp fangs project from the upper jaw. These contain a tube through which is forced the poison secreted in the poison glands near the root of the tooth. When the snake strikes at its victim, the sharp ends of the fangs are buried in the flesh, and the poison is left in the wound. In some of the groups of mammals (that is, animals which are covered with hair) certain types of teeth are developed to an extraordinary degree, and by these teeth the animal is especially adapted for securing and masticating its par- ticular kind of food. Eabbits, squirrels, rats, and beavers have long chisel-shaped incisors which enable them to obtain their food by gnawing. These incisors grow throughout the life of the animal and are kept sharp by a constant grind- ing upon each other of the cutting edges. Canine teeth are altogether wanting in these rodents (Latin rodere = to gnaw). Following is the dental formula of the rabbit : — Canine teeth are specially fitted to tear in pieces fleshy tissue, and they reach their greatest development in the group of car-niv'o-ra or flesh-eaters. The long, conical teeth in the jaws of the dog, cat, lion, and tiger are canines. All the teeth of the carnivora have pointed crowns adapted for tearing and cutting, rather than for grinding. A most striking example of canine teeth is furnished by the huge A STUDY OF BLOOD MANUFACTURE 111 tusks of the walrus. The arrangement of teeth in the mouth of a dog is represented in the dental formula, .3 + 3 1+1-4+4 TO2+2_42 ' ~ Iii the group of the her-biv'o-ra} which includes the animals that feed wholly upon vegetation, the huge premolars and molars are of special use ; they grind up the grass and grain like millstones. A horse's dentition is represented by the formula, 3+3 1+1 4+4 3+3 _dl 3+3' T+i' P 4+4:' S+S~ The incisors of a horse are well developed, but the canines seldom push through the gums. In the space between the incisors and premolars, man puts the horse's bits. A cow has no incisors in the upper jaw, and the canines are also wanting. Since man has all of the four kinds of teeth developed in about equal proportions, he is evidently well fitted to eat both animal and vegetable tissues, and a well-rounded diet should include a great variety of food materials. The Tongue in Other Animals. — The tongue of frogs and toads is attached just inside the mouth opening, and its free end, when the mouth is closed, extends backward toward the gullet. In securing the insects upon which it largely feeds, the animal opens its mouth and thrusts forward the sticky end of the tongue, which captures the fly or bee. The end of the tongue is then quickly withdrawn into the mouth, and the food is swallowed at once. The snake uses its forked tongue principally as an organ of feeling, darting it from its mouth with great rapidity. This tongue is per- fectly harmless. Among the carnivora the upper surface of the tongue is covered with strong papillae. This enables the dog, cat, lion, or tiger to scrape the meat from bones and to extract the marrow after the bones are broken open. 112 STUDIES IN PHYSIOLOGY ---Mouffr fftffry/?* ope/7//fgs Ganglia co/ist/tt/t/ng- ~ ~ . dosser? surface. x FIG. 38. — The Earthworm. A = side view of an earthworm. B = dorsal view of a dissected earthworm. (7 = longitudinal section of an earthworm. The Alimentary Canal of the Earthworm. — At the anterior end of the worm is a small slitlike mouth opening, which communicates with the pharynx. By means of this more or less barrel-shaped organ the animal sucks in its food. Pos- A STUDY OF BLOOD MANUFACTURE 113 terior to the pharynx is the gullet ; it extends from about the sixth to the fifteenth joint of the body, and there opens into a thin-walled enlargement of the alimentary canal called the crop. From this storage sac the food mass is passed on into a muscular gizzard, where it is rolled about and ground to prepare it for digestion. The remainder of the food canal, the stomach intes- tine) extends from the nineteenth joint to the end of the body. Here the food is di- gested and ab- sorbed, The Alimentary Canal Of the Frog. FIG. 39. — Internal Organs of the Frog. — In the frog we fin d a more highly developed alimen- tary canal than that just de- scribed. Seven openings com- municate with the mouth cavity, cor- responding in function to the seven in the throat of man. These open ings are as follows: two from the nostrils, the mouth opening, two communicating with the ear cavities through the Eustachian tubes, the opening into the gullet, and the glottis (opening into the larynx). The frog, there- fore, has no distinct throat cavity. A short gullet conducts the food into the cylindrical stomach, and a somewhat coiled intestine communicates with the exterior of the body through the rectum. The frog has a well-developed liver, a = stomach. 6 = urinary bladder. c = small intestine. d = large intestine. e — liver. /=bile duct. g = gall bladder. h = spleen. i = lung. k = larynx. I = fat body. m = spermary. n = ureter. o = kidney. p = pancreas. r = pelvic girdle. * s = cerebral hemisphere. sp = spinal cord. t = tongue. u — auricle. v = ventricle. w = optic lobe. x = cerebellum. y = Eustachian recess. z = nasal sacs. 114 STUDIES IN PHYSIOLOGY beneath which is a green gall bladder. A pancreas is like- wise present, which, as in man, pours its secretions through the common bile duct into the small intestine. The alimen- tary canal of the frog is several times the length of the body, and hence it is more or less coiled. This increased length provides a greater surface for digestion and ab- sorption. The Alimentary Canal of the Pigeon. — Striking modifica- Cer*6ra/ ' fiem/spfteres ---Gutter ---Crop " "- <5yr/'nx "-/tight avr/'c/e FIG. 40. — Longitudinal Section of a Bird. tions, due to the absence of teeth in the mouth, are seen in the digestive apparatus of birds. In the first place, the gullet is relatively large to allow the passage of the more or less solid food. Two thirds of the way down the gullet on its ventral surface is a saclike enlargement of considerable size A STUDY OF BLOOD MANUFACTURE 115 called the crop. Here the food is softened somewhat, and then it is passed on into the stomach. This organ consists of & pro- ven-trie'u-lus (Latin pro = before + ventriculus = little stom- ach), the walls of which contain a large number of gastric glands, and a thick-walled, muscular gizzard, which has a horny lining. In the gizzard the food is ground, and this process is assisted by the small stones that the bird swallows. The intestine leaves the gizzard close to the opening from the pro ventriculus, and forms a loop inclosing the pancreas. The rest of the intestine is coiled in a more or less spiral fashion. A gall bladder is absent; the bile ducts for this reason pass directly from the right and left lobes of the liver into the intestine. The Alimentary Canal of the Sheep. — The majority of mam- mals have as a „. stomach a simple sac. But in some of the hoofed animals (cattle, sheep, goats, deer), this organ reaches a high degree of complexity. The FIG. 41. — Stomach of an Ox (opened to show grass eaten by Chambers). these animals is a = esophagus, d = psalterium. i .,T -,. 6 = rumen. e = abomasum. mixed with saliva c = reticulum. /= small intestine. and swallowed without mastication into a large sac called the ru'men. It is either stored here or is passed on to a second sac, called from its honeycombed wall the re-tic'u-lum. When the sheep or cow has finished eating, the food in rounded masses is forced back in lumps through the esophagus into the mouth cavity, and is then thoroughly masticated. To this process is given the name cud-chewing or ruminating. The pasty mass is now swallowed a second time, passing almost imme- diately into a third compartment of the stomach, the psal- 116 STUDIES IN PHYSIOLOGY terri-um. After being strained between the leaflike plates of mucous membrane in this sac, it enters the fourth and last chamber, called the ab-o-ma'sum. This is the real diges- tive portion of the stomach. The other sacs should be regarded, like the crops of birds, as enlargements of the esophagus that serve as storage reservoirs. The rennet used in making cheese is prepared from the lining of the abomasum of a calf. The wall of the rumen and reticulum of cud-chewing animals is eaten in the form of tripe. The intestines of the ox have the astonishing length of one hun- dred and fifty feet. Since the food of the animal is wholly vegetable, a much longer time is required for its digestion, and hence the great extent of the intestines. Carnivorous animals, on the other hand, have a relatively short alimen- tary canal. Comparison of the Digestive Organs Studied. — The striking characteristic of the digestive apparatus of the earthworm is its simplicity. A straight tube extends from one end of the body to the other, with several enlargements in which certain processes are carried on. Digestive glands corre- sponding to the liver and pancreas of man are altogether wanting. In the other animals that we have considered an increasing complexity of structure is seen until we come to the highly specialized alimentary canal of the ruminants. In every example studied the digestive organs have become specially fitted to digest the kind of food the animal eats. CHAPTER VII A STUDY OF THE BLOOD 1. USES OF THE BLOOD Nutrition in the Amoeba. — The process of nutrition in the amoeba is relatively simple. When the single cell, by push- ing out its false feet, comes in contact with a bit of food, the protoplasm of the animal slowly flows about the food FIG. 42. — An Amoeba taking in a Particle of Food. particle until the latter is surrounded. Once within the cell, the food is digested by the living substance, and, as the animal is continually altering its shape, this digested food is easily moved from one part of the cell to another. The animal is so small it has no need of a specially devel- oped alimentary canal or blood system. Oxygen is absorbed by the protoplasm as fast as it is needed, and the waste matters (carbon dioxid, water, and urea), that are always formed in living substance, are given off by the amoeba as fast as they are produced. Every part of the cell may be said to perform the functions of mouth, stomach, and intes- tine, of blood, respiratory, and excretory systems. Nutrition in Man. — In the human body, on the other hand, we find special organs, each devoted to but one of the 117 118 STUDIES IN PHYSIOLOGY functions we have just enumerated. The alimentary canal prepares the digested food, the lungs supply us with oxygen, while the waste matters are excreted by the kidneys, lungs, and skin. But every cell of the body, as was the case in the amoeba, requires a supply of nutrients and oxygen, and in every bit of living substance waste materials are being constantly formed by metabolism. Since many tissues of the body are at a considerable distance from the organs of diges- tion, respiration, and excretion, we can see that some means must be provided for bringing all these organs into commu- nication with each other. This is effected by the blood, which is pumped through blood vessels by the heart. In this way blood is able to serve the needs of every tissue of the body. Uses of the Blood. — Blood, therefore, has four important functions: (1) it carries the digested food from the alimen- tary canal to the various tissues that need it; (2) it absorbs oxygen in the lungs and distributes this gas to the working tissues ;• (3) it receives from the cells of the body the carbon dioxid, water, and urea that are produced by oxidation, and carries these wastes to the excretory organs, by which they are thrown out of the body ; (4) it helps also to equalize the temperature of the different parts of the body. 2. A STUDY OF BEEF-BLOOD l Preparation. — Blood is much the same in all mammals, and so we can learn a great deal in regard to this important tissue in our own body by studying the blood of a cow. One can secure at any slaughterhouse beef-blood, which should be allowed to flow from the animal into a bottle, and to stand in a cold place undisturbed for several days. When first drawn from the animal, it is a liquid of bright red color, but it soon changes to a dark maroon. Blood Clot. — Other changes are likewise noticeable. At 1 See "Laboratory Exercises," No. 25. A STUDY OF THE BLOOD 119 the end of a few moments the blood becomes viscid ; it soon thickens to the consistency of jelly, and if the bottle be now inverted, none of the blood will escape. An examina- tion made at the end of several hours shows that the jelly- like mass is gradually shrinking in size iintil finally it comes to occupy about half the capacity of the bottle. This dark red mass is called the blood clot, which retains the shape of the bottle, and by its form and color reminds one of a jar of currant jelly. Blood Serum. — If the blood is not disturbed for several days, a transparent, straw-colored liquid will be seen sur- rounding the clot and filling the other part of the space in the bottle. To this liquid is given the name blood serum. Blood, then, when taken from the body becomes separated into two nearly equal portions, the jellylike clot and the liquid serum, and to this process of separation is given the name co-ag-u-la'tion or blood clotting. Cause of Coagulation. — When- one examines with a com- pound microscope a drop of fresh beef -blood, red and white corpuscles similar to those described in human blood (see p. 25), are seen floating in the liquid plasma. In a short time, however, little threadlike fibers make their appearance in the serum, and extend in all directions across the drop. These soon shorten. In this process the red and white cor- puscles are gathered together as though caught in the threads of a net. The liquid serum, meanwhile, is squeezed out of the mass. This same process takes place in the bottle of beef-blood. The fibers at first extend from one side of the glass to the other, thus forming a more or less solid mass, which holds the blood in the bottle, even when it is inverted. The fibers soon shorten and lose their hold upon the glass, and by their shrinkage the cylindrical clot is formed. . Blood Fibrin. — We have seen that coagulation is caused by the fine threads that appear spontaneously as soon as blood is shed. Still clearer proof that this is the fact is furnished by the following experiment. Get the butcher at 120 STUDIES IN PHYSIOLOGY the slaughterhouse to catch a quart of freshly drawn blood, and to stir it vigorously for several minutes with a bunch of twigs or a broom. On examining the twigs one sees that they are covered with a stringy mass. When this is washed, it is found to be composed of white elastic fibers, like those we saw forming in the drop of blood under the compound microscope. By testing this so-called blood fibrin with nitric acid and ammonia, we demonstrate it to be a kind of proteid. Defibrinated Blood. — After the fibrin has been removed, a red liquid remains that looks like the normal blood. But however long it is allowed to stand, it will never clot. The name de-fi'bri-na-ted blood (Latin de = without +fibriri) is given to this liquid. So then we have proved in two differ- ent ways that the clotting of blood is due to blood fibrin. Difference between Blood Plasma and Blood Serum. — We have called the freshly drawn liquid in which the blood cor- puscles float, the blood plasma, and the straw-colored liquid surrounding the clot, blood serum. While the appearance of both liquids under the compound microscope is much the same, they differ in one particular : blood plasma clots, blood serum does not. Or to describe their difference in composi- tion, we may say that blood serum is blood plasma minus fibrin. The question naturally presents itself, Why does not blood plasma clot when it is in the body? Physiologists have demonstrated that coagulation is not due to the fact that the blood has ceased to be in motion, nor is it caused by exposure to the air. It is known that a liquid proteid called fi-brin'o-gen (Latin fibrin-}- gen = maker) is found in blood plasma, and that this is changed into solid fibrin when a clot is formed. But why this change does not take place as long as the blood is within a healthy blood vessel, has not been satisfactorily explained. Composition of Blood Serum. — Blood serum contains over 90 % of water, in which are dissolved the various nutrients obtained by absorption from the alimentary canal. The A STUDY OF THE BLOOD 121 presence of each of these nutrients in the beef serum may be demonstrated by applying the various tests given on pp. 44_46. Thus, if a small portion of the serum be put into a test tube and heated, it coagulates, showing that pro- teids are present. The occurrence of mineral matters is proven by the ash that is left after blood is burned. Grape sugar and fats are likewise present, though in smaller quantities than one would expect. Starch is, of course, absent. Change in Blood on mixing with Oxygen. — When the blood passes through the lungs, as already stated, it absorbs oxy- gen. The resulting change in color can be seen from the following experiment. Pour a small amount of defibrinated blood into a glass bottle and stopper tightly. When the bottle is shaken vigorously, the blood is mixed with the oxy- gen in the bottle, and the dark maroon color changes almost instantly to a bright scarlet. The same change in color takes place when the serum is poured off and the blood clot is exposed to the air. 3. HUMAN BLOOD Application of the Study of Beef -blood. — All of the facts learned from the preceding study of beef-blood are equally true of human blood. As soon as it flows from the body, the fibrinogen changes to fibrin, and thus a clot is formed. Coagulation is of great practical importance, since it provides a natural means of closing up injured blood vessels, and of preventing loss of blood. Red Blood Corpuscles. — The form and size of red blood corpuscles have been already discussed in connection with the study of the cellular structure of the body (see p. 26). When highly magnified they appear as circular disks, the color of which is not red, as one would expect, but yellowish. The deep red color of the blood is due to the fact that every drop contains such a countless number. Like other cells they are composed of protoplasm. Chemt 122 STUDIES IN PHYSIOLOGY ^8,%°C»^o cal analysis shows the presence of 50 % of water and a small amount of mineral matter. But the most important ingredient is a proteid substance called hem-o-glo'bin (see p. 18). This compound contains iron, and constitutes over 35 °/o of red corpuscles. Hemoglobin gives the red color to the blood and has the remarkable power of combining with oxygen when that element is abundant, and of giving it up wherever it is needed in the various parts of the body. We may, therefore, compare the blood corpuscles to countless little boats, floating in a stream of plasma ; they take on their cargo of oxygen from the air in the lungs and discharge it to the cells of the tissues. Wrorn-out cor- puscles are destroyed in the liver and spleen, \u yjy an(j their place is P/ taken by new ones, which are produced, as we shall learn, by cells in the red mar- row of bones. White Corpuscles. — We have seen that white corpuscles re- semble amoebas in their structure and activities. Let us now study their functions in the human body. When one gets a sliver of wood in one's finger and leaves it there for a time, the finger becomes more or less swollen and sore, and white pus or "matter" usually forms in the region of the wound. All these effects are probably due to the presence of bacteria, which were carried into the wound on the piece of wood. Finding in the tissues favorable conditions for growth, these w*ss|5«? FIG. 43. — Human Blood Corpuscles. Magnified about 200 times. Photographed through the microscope. The circular disks are the red corpuscles. Near the bottom of the photograph is a single white corpuscle of larger size. A STUDY OF THE BLOOD 123 minute organisms multiply rapidly and produce poisons called tox'ins, that cause the inflammation. As soon, however, as these inflammatory processes begin, great armies of white cor- puscles are hurried to the spot and proceed to attack the invading bacteria. If the FIG. 44. - White Corpuscles. number of germs is relatively small, and if the corpuscles are in a healthy condition, the latter seize upon and devour the bac- teria in the same way that a = a white corpuscle devouring a bac- an amoeba takes in its food. terium. Under these conditions lit- & = a white corpuscle destroyed by bac- tie if any pus is formed. But if the bacteria get the upper hand in the struggle, many of the corpuscles are killed, and it is the dead white cor- puscles that form the pus. Amount of Blood in the Body — Blood constitutes about one thirteenth of the weight of the body; hence, in an adult weighing one hundred and fifty pounds there would be a little less than twelve pounds of this tissue. Ordinarily the blood is distributed about as follows : — one fourth in the heart, lungs, large arteries, and veins, one fourth in the liver, one fourth in the muscles attached to the skeleton, one fourth in the other organs of the body. 4. THE HYGIENE OF THE BLOOD Conditions Affecting the Red Corpuscles. — Since supplying oxygen to the various tissues is the function of the red corpuscles, it . is very important that their number be suffi- cient and that they be kept in a healthy condition. To this end, an abundance of sleep, exercise, fresh air, and nutritious 124 STUDIES IN PHYSIOLOGY foods are the essential conditions. Every one is familiar with the fact that the face looks pale after loss of sleep, or when food and fresh air are insufficient, or during periods of physical inactivity, and this appearance indicates a lack of red corpuscles. Habitual paleness, or a-nai'mi-a, is a disease requiring medical treatment. It is frequently due to a want of iron in the system ; hence, the efficacy of tonics containing this element. Fresh air, a moderate amount of exercise, and good food are usually the best remedies for ansemia. A good complexion is, therefore, very largely dependent on healthy blood. Paint, powder, and other cosmetics will not give such a complexion ; and besides cheapening the individual who uses them habitually, they are often a source of permanent injury to the skin and blood. Conditions affecting the Serum All the nutrition of the tissues is derived from the blood, and all the nutrients of the blood come from the foods we eat. If these foods are insufficient or of an improper kind, the serum will of course be deprived of necessary ingredients, and the organs must inevitably suffer in consequence. Hunger and thirst are the sensations that tell us the blood is in need of new material (see p. 294). That this is true is proven conclusively by the fact that these sensations disappear when water and liquid food, instead of being swallowed, are injected directly through the skin into the blood vessels. In supplying material for the blood, however, one must not follow en- tirely the dictates of taste. For instance, if one is very thirsty, one is tempted to drink rapidly a great quantity of ice-cold liquid, when a smaller quantity of water, in passing slowly through the mouth, will alleviate the thirst much sooner and more completely. The importance of eat- ing proteid foods cannot be emphasized too often. Healthy blood should contain 8 % to 9 % of this kind of nutrient, and its place can never be filled by the sometimes more palatable sugars, starches, or fats. A STUDY OF THE BLOOD 125 *&£& i't&t 5. A COMPARATIVE STUDY OF BLOOD Animals without Blood. — Anioebas and other single-celled animals, as we have seen, have no blood. In the sponges, sea anemones, and jellyfishes, also, there is no distinct tissue that can be called blood, since absorption of food, respira- tion, and excretion can be carried on throughout the whole of the interior surface of these animals. All the other groups of animals have some kind of a circula- Color of the Blood. — Many of the inverte- brates (animals having no backbone) have color- less blood. There are, however, exceptions to the rule. In lobsters and other so-called " shell- fish," for example, blood is bluish, while in worms it is reddish, yellowish, or greenish. In nearly every vertebrate the blood is red. Temperature of the Blood. — The body tem- perature of a human being in health is 981° Fahrenheit, and this is of course the temperature of the blood. In fever this sometimes rises to 105° or even 109°; in other diseases the temperature may decrease a degree or more, but any greater variations from the normal are usually fatal. In birds the blood is about ten degrees warmer than it is in man (i.e. 108° F.). Keptiles (snakes, turtles, and alligators), am- phibia (that is, animals living the first part of their life in water and the adult period on land, for example, frogs and Fi«. 45. — Corpuscles of Frog's Blood. Magnified about 50 times. Photographed through a microscope. The oval disks with the dark nuclei are the red corpus- cles. In the center are the nuclei of two white corpuscles of smaller size. 126 STUDIES IN PHYSIOLOGY toads), and fishes are called cold-blooded animals. In re- ality these animals have the same temperature as their sur- roundings, and since these surroundings are usually cooler than the 981° of man, these animals feel cold to the touch. White Corpuscles — Even in colorless blood there are cells corresponding to the white corpuscles of man which have the power of altering their form by amoeboid movement. FIQ. 46. —A Comparison of Red Corpuscles. We may, then, regard white corpuscles as a constant con- stituent of blood in all animals. Red Corpuscles. — Ked corpuscles are found in nearly all vertebrates and in vertebrates only; but in the various groups there are striking differences in their form and size. Fishes, amphibia, reptiles, and birds usually have oval red corpus- cles which always have a nucleus. In man and other mammals no nucleus is seen in completely formed corpus- cles, although the cells in the red marrow of bones from which they are formed do have a nucleus. All mammals A STUDY OF THE BLOOD 127 have circular red disks, with the exception of the camel family, in which they are oval. In a given species of ani- mals the diameter of red corpuscles is pretty constant, but one finds great variations in size in a comparative study. A kind of amphibian (Proteus) has the largest known corpus- cles; the smallest are found in the musk deer. Among birds the size is proportional to the size of the animal, being largest in the ostrich and smallest in the humming bird. In murder trials a practical use is made of these striking differences in red blood corpuscles. If blood stains are found on an implement or an article of clothing, microscopical ex- amination can sometimes decide to what animal the corpus- cles belong, and in many cases this evidence decides whether there shall be conviction or acquittal of the accused. 6. CHEMICAL COMPOSITION OF BLOOD A. Solid ingredients. 1. Red corpuscles, composed of — a. Water, 50%. b. Hemoglobin, over 35%. c. Mineral matter, etc., 5%. 2. White corpuscles, composed of a. Water. b. Proteids. c. Mineral matter. B. Liquid ingredient == blood plasma, composed of — 1. Fibrinogen, which changes to fibrin, Forming the Blood Clot. 2. Blood serum, composed of a. Water, about 90% < b. Proteids, about 8% to Absorbed from Alimentary Canal. * c. Fats, sugars, and mineral matters, from 2% to 1% < — d. Urea and water, wastes obtained from tissues and carried to excretory organs. 128 STUDIES IN PHYSIOLOGY C. Gaseous ingredients (combined with other ingredients of blood). 1. Oxygen, obtained in the lungs and carried to the tissues by the hemoglobin of the red corpuscles. 2. Carbon dioxid, obtained from the tissues and carried by the blood plasma to the lungs, where it is excreted. CHAPTER VIII A STUDY OF THE CIRCULATION OF BLOOD Definition of the Circulation — We have seen in the pre- ceding pages that the blood takes up oxygen in the lungs, that it absorbs food materials while coursing through the villi of the intestines, and that it loses waste materials in the excretory organs. It is evident, therefore, that this important liquid must be kept moving from one organ to another. By the term circulation of the blood is meant the ceaseless movement of the blood through a system of tubes called blood vessels. Organs of Circulation. — The force that drives the blood around through the body is furnished by the contraction of the muscular walls of the heart. Any blood vessel that carries blood away from the heart is called an ar'te-ry (Greek aer = air -+- terein = to hold, — a name which was given by the early anatomists to those tubes because they were found empty after death, and were therefore supposed to carry air). TJie veins are the blood vessels that bring the blood back to the heart. Connecting the arteries and the veins in every part of the body are countless microscopic blood vessels called cap'il-lar-ies (Latin eapi#tt*=hair, so called from their minute size). 1. THE HEART1 Position, Shape, Size. — If any one closes upon the palm the fingers of his right hand and places his fist in the middle of his chest in such a way that his thumb points obliquely 1 See "Laboratory Exercises," No. 27. K 129 130 STUDIES IN PHYSIOLOGY P.K downward toward the left side, the fist will represent ap- proximately the size, shape, and position of the heart. To be more exact, one may describe the heart of an adult as a conical organ, IX*. five inches in length. It lies diagonally be- hind the breast- bone, near the middle of the chest cavity, with its pointed end or apex ex- tending toward the left side be- tween the fifth and sixth ribs. Since the beat of the heart is felt most plainly near the apex, it is commonly but erroneously believed that the heart lies on the left side of the body. Let one imagine the front wall of the chest cav- ity to be re- moved; one FIG. 47. — Ventral View of Heart, Large Blood Ves- sels and lungs. Ao = aorta curving toward left. B = bronchi to lungs. (7= carotid arteries. L.A. = left auricle. L.J.V. = left jugular vein. L.L = left lung. L. V= left ventricle. P. A = pulmonary artery dividing into two. P. V= pulmonary veins. R.A = right auricle. R.J.V= right jugular vein. R.L = right lung. R. V— right ventricle. S.C. = arteries and veins supplying shoulders and arms. T — trachea or windpipe. V.l = inferior vena cava. V.S = superior vena cava. would then see the soft, pink lungs on either side, nearly filling the chest cavity, and between them the heart (see Figs. 4 and 47). The Pericardium. — The heart is not only surrounded by the A STUDY OF THE CIRCULATION OF BLOOD 131 skeleton and muscles of the chest wall and by the lungs, but it is also inclosed in a tough bag of connective tissue called the per-i-car'di-um (Greek peri = around + cardia = heart). This sac is attached to the heart only at its upper or larger end. In size it is considerably larger than the organ it surrounds, and hence the heart has plenty of room in which to expand and contract unhindered. The inner layer of the pericardium and a thin outer layer of the heart (which is continuous with the pericardium) are both formed of smooth, glistening se'rous membrane, which secretes just enough liquid to allow the heart to move freely within its case. The Heart a Double Organ. — When one makes a dissection of the heart, one finds it to be composed of two halves which are completely separated from each other by a muscular par- tition. It will help a great deal toward understanding the circulation of the blood if this fact is kept constantly in mind, and hereafter the two halves of the heart will be referred to respectively as the right heart and the left heart. The Cavities of the Right and Left Hearts. — Each heart is divided by a movable partition into an upper and smaller chamber, called the au'ri-de, and a lower chamber called the ven'tri-de (see Figs. 47, 48, 49). An examination of the outside of the heart shows the significance of these terms ; for, at the upper or larger end are the two small ear-shaped auricles (Latin auris = ear -|- cula = little), while at the apex are the ventricles which, taken together, doubtless reminded the early anatomists of a small stomach (Latin venter = stomach + culus — little). A comparison of these four chambers shows important differences. In the first place, the auricles have relatively thin walls as compared with the ventricles, and the reason for this is evident when we see that their function is simply to receive the blood from the veins and to push it downward into the ventricles. When one compares the walls of the left ventricle with those of the right, one is struck with the 132 STUDIES IN PHYSIOLOGY great thickness of the former. The left ventricle does much more work than the right ; it forces blood to the top of the head, to the tips of the fingers and toes, and to every other organ of the body. The right ventricle, on the other hand, pumps blood only to the lungs. The Valves of thie Right and Left Hearts. — We have described the partition between the auricles and ventricles as mov- able. In the right heart there are three triangular flaps of connective tissue, attached to the sides of the opening from FIG. 48. — Right Heart (opened) . FIG. 49. — Left Heart (opened) . auricle to ventricle. This is the so-called tri-cus'pid valve (Latin tri= three + cuspis = point). When the ventricle is empty, these flaps tang downward ; but as the blood pours in from the auricle, their free edges gradually float upward until, when the ventricle is full, the three portions come to lie horizontally. It is evident that when the ventricle begins to contract, the blood would tend to push this valve upward still further, thus allowing the blood to return to the auricle. This is prevented, however, by a number of strong cords of connective tissue (the chor'dce ten-din' e-ce), that are attached at one end near the movable edge of the A STUDY OF THE CIRCULATION OF BLOOD 133 valve flaps, and at the other to muscular elevations (the pap'iUa-ry muscles) on the inner walls of the ventricle. The length of the cords is regulated by these muscular papillae in such a way that in a healthy heart the valves, when closed, do not allow a drop of blood to return to the auricle. In certain kinds of heart disease these flaps do not act prop- erly, and then the skilled ear of the physician, listening at the wall of the chest, can detect at each heart beat the " murmur " caused by the backward rush of the blood. The valve in the left heart works on the same principle as the tricuspid valve we have just described. It consists, however, of but two flaps. From its fancied resemblance to a bishop's mitre it has received the name ml'tral valve. The Blood Vessels connected with the Right Heart. — The function of the right heart, as we have already suggested, is that of pumping the blood, received from the various organs of the body, to the lungs. Connected with the right auricle 'are two large blood vessels ; one brings in the blood from the organs in the lower part of the body (liver, stomach intes- tines, kidneys, feet), and is called the in-fe'ri-or ve'na ca'va (Latin inferior = lower -f cava = hollow + vena = vein) ; the other, the su-pe'ri-or ve'na ca'va, pours into the right auricle the blood from the head, the arms, and the upper part of the trunk. All this blood is a dark red or purplish color, because it has given up its oxygen to the various tissues from which it has come. It must therefore load up with oxygen be- fore it can again supply this ever needed element. The new supply of oxygen is secured in the lungs. From the right auricle the blood first goes into the right ventricle ; then it is forced into a large blood vessel called the pul'mo-na-ry artery (Latin pulmonarius, referring to the lung). Soon after leaving the heart the pulmonary artery divides, giving off a branch to each lung (see Figs. 47—49). The Semilunar Valves. — The pulmonary artery is always full of blood, and when the ventricle contracts, this blood ves- sel has to be stretched in order to accommodate the additional 134 STUDIES IN PHYSIOLOGY blood that is forced into it. Hence, when the ventricle begins to relax, the blood tends to rush back into this chamber from the pulmonary artery. To prevent this three sem-i-lu'nar valves (Latin semi == half -f luna = moon) are placed at the opening of the artery. Each valve is shaped like a watch pocket. The three open outward from the heart, but as soon as the ventricle begins to relax, the blood fills up the pockets, and the three valves, by meeting in the middle of the artery, keep the blood from returning to the ventricle (Figs. 49 and 50). The Blood Vessels connected with the Left Heart. — : After receiving oxygen in the lungs, the scarlet blood is brought to the left auricle by four pulmonary veins (Fig. 49). It is then forced into the left ventricle and out into the a-or'ta, which is the largest artery of the body. Branches of this aorta supply blood to every part of the body from the crown of the head to the tips of the toes (Fig. 56). At the opening of the aorta are three semilunar valves, which work just like those in the right heart. The Beat of the Heart. — If one etherizes a frog, and then opens the chest cavity, one can watch the regular beating of the heart. First the two auricles contract at the same time, becoming paler in color, thus showing that the blood has been forced down into the ventricle. As soon as the auricles have ceased to contract, the apex of the heart (con- taining the ventricle) begins its work, driving the blood out into the pulmonary artery and the aorta. Meanwhile, the auricles have been relaxing and filling with blood. When the ventricle has emptied itself of blood, it also relaxes. If one feels of the heart at this time, it is found to be soft and flabby, while during contraction it is hard. The action of the human heart is much like that described for the frog. Each heart beat, therefore, consists of a contrac- tion of the two auricles, followed by a contraction of the ventri- cles; then comes the relaxation of the muscular walls and a pause , in which the chambers arejilled with blood. A STUDY OF THE CIRCULATION OF BLOOD 135 The Action of the Valves of the Heart. — Let us now review in succession the events that occur within the chambers of the heart from the beginning of one heart beat to the begin- ning of the next. The walls of the auricles begin their con- traction in the region where the veins are bringing in the blood. In this way the blood is prevented from being pushed backward, and all of it is forced into the ventricles. As long as the auricles are contracting, the mitral and tricuspid valves are at least partly open; but when this contraction ceases, these valves are forced by the ji blood in the ven- tricles into a horizontal posi- tion, but are prevented from going farther by the chordae ten- dineae and the papillary mus- cles. Mean- while the semi- lunar valves are kept closed by the pressure of the blood in the aorta and pulmonary artery, and for an instant the blood is held fast in the grip of the ventricles. The contraction of the ventricles now begins, and the pressure on the two sets of valves increases. The mitral and tricuspid valves, that close the passage back to the auri- cles, cannot open, and so the semilunar valves are forced back, and the ventricles drive on the blood they have held into the two large arteries (pulmonary and aorta) already mentioned. During the contraction of the ventricles the auricles have been relaxing and filling with blood. When the ventricles A B FIG. 50. — Diagrams to show the Action of the Valves of the Heart. A = position of valves during pause. B = position of valves during the contraction of the ventricle. 136 STUDIES IN PHYSIOLOGY relax, the semilunars close, the mitral and tricuspid valves open, and the blood passes into these lower cavities. For a very short time, therefore, blood can flow freely from the mouth of the veins, through the auricles, down into the ventricles. But as the latter fill, the valves float up toward a horizontal position. Then comes the contraction of the auricles, which begins the whole series of events just de- scribed. We may summarize as follows what we have learned in regard to the action of the valves : (1) when the auricles contract, the mitral and tricuspid valves are open and the semilunar valves are closed ; (2) when the ventricles con- tract, the semilunar valves are open and the mitral and tricuspid valves are closed ; (3) during the pause before the beginning of the next heart beat, the mitral and tricuspid valves are open, and the semilunar valves are closed [as Sounds of the Heart. — If one listens at the chest wall, one can hear two distinct sounds during each heart beat. The * first sound is longer and more muffled ; it may be compared to the syllable lub, and is probably caused by the vibration of the valve flaps and the chordae tendineae when the contraction of the ventricles closes the mitral and tricuspid valves. The second sound is short and sharp, like the syllable dup. It follows the contraction of the ventricles and is due to the quick closing of the semilunar valves by the pressure of the blood in the arteries. The Blood Supply for the Heart. — One of the hardest worked organs of the whole body is the heart. During every minute of our lifetime it contracts from sixty to a hundred and twenty times, and the only time it gets for rest is during the pause of a fraction of a second after each heart beat. The heart muscle must, therefore, be oxidized to furnish energy for all this work, and consequently new building material must be continually furnished. An abundance of blood passes through the cavities of the heart, but the walls A STUDY OF THE CIRCULATION OF BLOOD 137 are so thick that none of it can soak out into the muscle even if there were time to do so. Just beyond the semilunar valves of the aorta, two arteries (the cor'o-na-ry arteries) are given off ; these at once pass over and through the walls of the right and left hearts (like a crown; hence, Latin corona = crown), sending branches into every part of the working tissue. 2. THE BLOOD VESSELS Position of Arteries and the Pulse. — We have defined an artery as a blood vessel carrying blood from the heart. A V FIG. 51. — Cross Section of an Artery (A), and of a Vein (7). c — connective tissue. m = muscle layers. e.c = cells of serous lining. n = nuclei of serous cells. Every time the ventricles contract, we have seen that the aorta and pulmonary artery are stretched ; this is true of every artery in the body. Most arteries lie beneath thick layers of muscle or bone, which protect them from possible injury; but in certain regions of the body they run close to the surface. If one places one's forefinger on the wrist of one's other hand, just at base of the thumb, one can feel a dis- tinct beating, called the pulse. This is due to the enlarge- ment of the artery at each heart beat. When an artery is cut, therefore, the blood is forced out in spurts at each con- traction of the ventricle. Structure of Arteries. — If one cuts off a piece of the aorta of any animal, one finds that the blood vessel retains its 138 STUDIES IN PHYSIOLOGY tubular form. It can be stretched to a considerable extent ; but resumes its original form and size when the force is removed. In the cross section of an artery one can distin- guish three layers. The outer layer is formed of interlacing connective tissue fibers. Beneath this covering is a thick layer composed of muscular and elastic tissue. It is the elastic tissue that allows the arteries to expand when more blood is forced into them by the contraction of the ventricles. After each pulse these elastic walls squeeze the blood forward into the capillaries ; arteries, therefore, are specially adapted to keep the capillaries full of blood. The third layer forms a smooth lining for the tube ; it is composed of serous membrane (Fig. 51). Position of the Veins. — On the back of the hand one sees through the skin a branching system of blu- ish blood vessels. These are veins. Unlike the arteries, veins have no B FIG. 52. — Valves in a Vein. A = vein laid open to show pouch-shaped valves. B — section of vein, showing valve open by flow of blood toward heart. C= section of vein, showing valve closed pulse, as One can easily by flow of blood back toward ' capillaries. Prove bJ pressing one's finger upon one of them. Since blood flows slowly and steadily back to the heart through the veins, there is little danger of any consider- able loss of blood, even if some of them should be injured. Many veins lie near the surface, while most of the arteries, as we have just stated, are buried deeply among the other tissues. The Structure of Veins. — When the veins are emptied of blood, they immediately collapse. In a cross section of one of these blood vessels (as in that of an artery) can be seen three layers, connective tissue, muscular and elastic tissue, and the serous lining, but, as would be expected, each layer A STUDY OF THE CIRCULATION OF BLOOD 139 is much thinner than is the case in the walls of an artery (Fig. 51). Veins, however, are provided with valves shaped much like the semilunars of the aorta and pulmonary artery. The blood can flow toward the heart, but as soon as it begins to pass in the opposite direction, these valves are immedi- ately filled and thus the passage is obstructed (Fig. 52). If one ties a cord tightly about the wrist, one can see the veins swell, and small hillocks appear which indicate the position of the valves just described. Position of the Capillaries. — As we trace the arteries far- ther and farther from the heart, we see that they divide and subdivide until very small branches are formed. That these fine branches are still arteries is proved by the fact that elastic and muscular tissue are present in their walls. Fi- nally, however, these tiny blood vessels become continuous with still smaller tubes, the capillaries. So numerous are the capillaries that one cannot push the point of a needle for any considerable distance into any organ of the body without piercing a number of them. These smallest of blood vessels communicate freely with one another and form a complicated network of tubes that bring blood close to all cells of the body. As the capillaries begin where arteries end, so they end where the smallest veins begin. Throughout the body, therefore, is a continuous system of blood vessels. Importance of the Capillaries. — If the blood were kept con- stantly within this system of tubes, it would be entirely un- able to help in the nutrition of the body. Each cell must take from the blood the nutrients it needs for its special work; likewise it must give off to the blood the wastes it has formed by oxidation. It is through the thin-walled capillaries tlrnt all these exchanges of materials occur. Hence, the capillaries form the most important portion, of the blood system. We may regard the arteries as the sup- ply pipes for the capillaries, and the veins as the drain pipes from them. 140 STUDIES IN PHYSIOLOGY Structure of the Capillaries. — In structure the capillaries are extremely simple. At the points in the blood system where arteries end and capillaries begin, connective, mus- cular, and elastic tissues disappear. The walls of the capil- laries are continuous with the inner lining of the arteries and the veins, and are formed of a single layer of very thin cells'. We have in this arrangement the best possible con- ditions for the process of osmosis. Only the thin membrane of ^he capillary wall separates tLe blood from the surround- ing tissues, 1 and an ex- change of ma- terials be- tween the two is readily car- ried on (Fig. 53). Flow of Blood in the Web of a Frog's Foot.1 — One can easily watch the flow of the blood in the thin web of a frog's foot. If a 1 % solution of chloretone is forced into the mouth of the animal and its body is wrapped in a wet cloth, the frog will lie perfectly passive, and the thin membrane can be spread out and examined with the microscope. Under these conditions one can trace the blood current from the arteries through the capillaries, into the veins, and a most fascinating study it is. One can see in all of the tubes a large number of oval-shaped red corpuscles, and possibly here and there a more or less spherical white corpus- cle. These are carried along in the transparent stream of colorless plasma. In some of the larger vessels the current 1 See "Laboratory Exercises," No. 28. B AC FIG. 53. — Capillaries A = surface view. C— cross section. B = longitudinal section. d = interior of capillary. e.c = cells forming wall of capillary. n = nuclei of cells. A STUDY OF THE CIRCULATION OF BLOOD 141 is driven forward in jerks ; we, therefore, infer that we are looking at arteries. As the arteries subdivide and become smaller, the pulse gradually disappears, and in the capil- laries there is a steady stream on toward the veins. Some of the capillaries are so small that but a single corpuscle can pass through at a time; indeed, they are sometimes squeezed out of shape within the microscopic tube, but on escaping into the larger blood vessels they resume their former shape (see Fig. 54). Absence of Pulse in Capillaries and Veins. — It is clear that if the pulse were transmitted from the arteries to the capil- laries, the thin walls of the FIG. 54.— Capillaries of Frog's Foot, latter would be unable to with- The capillary tubes are more or less stand the pressure; the blood filled with the oval red corpuscles, would then escape from the The irregular black spots are the pigment cells which give color to capillaries and flood the vari- the skin of the frog. ous tissues. Hence, there must be some means of reducing the pressure in the blood vessels before the capillaries are reached. At least two causes combine to produce the even flow of blood in the capillaries and veins. In the first place, the arteries near the heart expand at every contraction of the ventricle, thus making room for the additional cupful of blood that is forced out at each heart beat. This expansion of the arteries, however, becomes less and less as the blood enters the smaller branches. In the second place, if all the fine capillaries of the body could be placed side by side, their combined diameters would be many times the diameter of all the arteries that supply them with blood. Hence, as the blood is pushed outward from the heart, it finds more and more room in which to flow. The size of each capillary is 142 STUDIES IN PHYSIOLOGY so small, however, that there is a great deal of friction, and the blood is therefore obliged to move more slowly. These two characteristics of structure explain the absence of a pulse in the capillaries. When the blood passes into the veins, its current is also slow and without any pulse. 3. THE CIRCULATION OF THE BLOOD Having completed our survey of the structure and action of the heart and the blood vessels, we are ready to study the blood system as a whole and to learn how the blood gets to, through, and from every organ of the body. The Two So-called Systems of Circulation. — In our study of the heart we always referred to the right and left hearts as though they were entirely apart from each other. Let us keep this distinction in mind in considering the circulation of the blood, for there are likewise two distinct systems of blood vessels. One system carries the blood to, through, and from the lungs; it is for this reason called the pulmo- nary circulation. The other system is known as the sys- temic, which supplies blood to every other portion of the body, that is, to the general system. The Pulmonary Circulation. — In order to understand the pulmonary circulation we need only review the facts we have already learned. The blood is driven by the contraction of the right ventricle past the semilunar valves into the pul- monary artery, which soon branches, giving off an artery to each lung. After passing through the finer pulmonary arter- ies and capillaries, the blood is finally collected by the -four pulmonary veins, which empty into the left auricle, whence the blood comes into the left ventricle (see Fig. 55). The Systemic Arteries. — From the left ventricle the blood stream is forced into the aorta. This great supply pipe of the body first arches over toward the left, like a shepherd's crook ; it then passes posteriorly through the dorsal part of the chest cavity and, piercing the diaphragm, it enters the abdomen. Three regions of the aorta, therefore, can be A STUDY OF THE CIRCULATION OF BLOOD 143 distinguished: first the arch of the aorta, second the thoracic or chest aorta, and third the abdominal aorta (Figs. o£ and 56). / Cff/}///ar/es of % Mews from faatf Lymphatics from- _ . bpper/wrt of body Opening of /ymfi/?fft/cs /ffto veins Sujoer/or vena cai/a- - - — Pu/mor/crry artery — --6 /?/§/? t OLi/ricfe - - /nfer/or i/er?aca/a -fj- Se/n/'/t/rtan/a/ves ^ lymphatics from--— cf> ofaorta to -\~1lu stofr?ach,sp/ee? Sp/eer? -tfarafict/ artery U/r/ar artery "*• Branches of aorta to kiofneys — Artery to /e$ /ferr/ora/j --- few from tea FIG. 56. — The Systemic Arteries (red) and Veins (blue). brings to the same auricle the blood from the lower part of the body. One portion of this lower venous system, however, requires special description. The Portal System of Veins. — The blood from the spleen, the pancreas, the stomach, and the intestines takes a somewhat 146 STUDIES IN PHYSIOLOGY roundabout course back to the heart. The veins from these four organs unite to form the large portal vein, which enters the liver, and there divides to supply a system of capillaries. These in. turn send the blood into the he-pat'ic veins (Latin hepaticus, referring to the liver), which empties into the in- ferior vena cava. The peculiarity of the portal system lies in the fact that the blood supplied by the aorta to these organs of the abdomen passes through two sets of capillaries before returning to the heart (see Figs. 55 and 36). In our study of the liver we learned that one of its most important functions is that of storing carbohydrate food in the form of glycogen. The portal system of veins is an adaptation to this function, for the blood from the stomach and the intestines is often well supplied with sugar which may be left for a time in the liver. Blood from the kidneys, on the other hand, has not been supplied with this nutrient, and so passes directly into the inferior vena cava. The liver, it will be remembered, contains one fourth of all the blood in the body, and this blood is of two kinds. One kind is furnished direct by a branch of the aorta (hepatic artery); the other kind comes to the liver through the portal vein. The latter is the only vein in the body that supplies blood to capillaries. The Circulation but a Single System. — To keep the course of the blood clearly in mind, we have carefully distinguished a pulmonary from a systemic circulation. In reality, how- ever, there is but a single circulation in the body. The blood cannot pass across from the right heart to the left heart. In order to get back to the right ventricle, for instance, a drop of blood must first go through a system of capillaries in the lungs, must return to the left heart, and must thence be driven through a second set of capillaries before it reaches the point from which it started. And if, perchance, this drop of blood goes through the tissues of the stomach or intestines, or, in other words, through the portal system, it must pass through three different sys- A STUDY OF THE CIRCULATION OF BLOOD 147 terns of capillaries before it can begin a second round of the body. Changes in the Composition of the Blood. — The composition of the blood is continually changing in its passage through the various tissues of the body. We may, perhaps, make clearer these various changes by expressing them in tabular form as follows : — In muscular, nerve, and other tissues, In lining of mouth, stomach, intestines, In lungs, In kidneys and skin, BLOOD LOSES Materials needed for growth, repair, and production of en- ergy. Materials needed for the manufacture of digestive juices (and for growth and re- pair). Carbon dioxid and water. "Water and urea. BLOOD GAINS Wastes formed by me- tabolism (carbon di- oxid, water, urea;. Digested nutrients (proteids, fat, starch, sugar, min- eral matters, and water) and wastes. Oxygen. Carbon dioxid. Inappropriateness of the Terms "Arterial" and "Venous." — Thus far we have avoided the terms ar-te'ri-at and ve'nous as applied to blood. These terms are commonly used in text- books, but they often give rise to considerable confusion. By arterial blood is meant the bright scarlet blood that comes back from the lungs to the left heart, whence it is distributed through the aorta to all parts of the body. The word arterial, however, suggests arteries, and orie easily jumps at the conclusion that arterial blood is always car- ried in arteries. This is not true ; the pulmonary artery carries the dark colored or so-called venous blood. In the same way venous blood is commonly supposed to flow only in veins ; but we must bear in mind that the pulmonary veins carry arterial blood. The difference in the color of the blood is due almost entirely to the amount of oxygen that is present. Hence, we may avoid all possible confusion by calling the bright scarlet blood ox'y-gen-a-ted blood, or blood 148 STUDIES IN PHYSIOLOGY rich in oxygen ; while the darker blood may be described as de-ox'y-gen-a'ted blood. The former is not necessarily pure blood, nor is the latter always impure. The purest blood of the body is undoubtedly the dark colored blood that pours into the inferior vena cava from the kidneys, for when it reaches the kidneys it has already lost in the lungs its carbon dioxid; in the kidneys the water and urea are removed. Regulation of the Blood Supply to the Various Organs. — Every one knows that the pulse beat is more rapid and the body feels warmer during vigorous exercise. The feeling of warmth is due to the more rapid metabolism that is going on in the muscles, and because of this metabolism there is need of a greater supply of blood to repair the wasting tissues. Since there is seldom more than twelve pounds of blood in the body of an adult, other organs must do without their usual supply if the working muscles are to receive the amount of blood that they need. It will be remembered that in the description of the arteries, the presence of muscle tissue was noted ; it is these muscles in each artery that de- termine its size. When a considerable amount of blood is needed, for instance, in the brain, the muscles of the arteries in this part of the body relax, and the vessels become larger. In other parts of the body, however, there must be at the same time a corresponding decrease in the size of arteries by the contraction of the circular muscles. All these changes in the diameter of arteries are regulated by the sympathetic nervous system. 4. THE LYMPHATIC SYSTEM The Lymph. — From our discussion of the structure and use of the capillaries, one might infer that the liquid nutri- ents of the blood pass directly from these thin-walled tubes into the tissue cells, and that waste substances are given off from the cells directly to the blood. In reality this is not true. In the tissues of the body there are countless small A STUDY OF THE CIRCULATION OF BLOOD 149 spaces, and as the blood passes through the capillaries, part of the plasma soaks out by osmosis and keeps these spaces filled with a watery liquid known as the lymph (Latin lymplia= water). Occasionally the colorless corpuscles work their way by amoeboid motion out between the cells of the capillary wall, and so escape into the lymph. One might, therefore, say that the tissues are bathed with lymph, which is really blood minus the red corpuscles, and considerably diluted ivith water. Changes in the Lymph. — Since this liquid is in immediate contact with the tissues, the cells can take from it the nutrients necessary for their growth and repair, and at the same time can unload into the lymph their use- less burden of waste matters. The lymph in turn gives off some of these waste materi- als to the blood and receives new supplies of nutritive ingredients. In this way the lymph acts as a middleman between the blood and the tissues. By this constant inter- change of materials the lymph in a given organ is kept tolerably constant in its com- position, but in different organs this liquid varies considerably. The Lymphatics. — The amount of lymph is constantly increased by the osmosis that goes on in the capillaries. Hence, if there were no provision for draining lymph back into the blood system, the tissues would become unduly dis- tended. Such is the case in the condition known as dropsy. This drainage is accomplished by a system of vessels known as the lym-phat'ics. The lymphatics begin as extremely mi- nute, thin-walled tubes, which open freely from the spaces between the cells. As the tubes pass out through the tissues, they unite to form larger vessels (see Fig. 57), and these FIG. 57. — Lym- phatics of the Right Arm. g lymphatic nodes. 150 STUDIES IN PHYSIOLOGY finally enter a duct of considerable size (the tho-rac'ic duct) which carries the lymph up ward -from the abdomi- -/ nal cavity, through the chest or thoracic cavity (see Fig. 58, a, 6). The thoracic duct finally emp- ties the lymph into a branch of the superior vena cava on the- left side of the neck (Fig. 58,/), and in this way the liquid that has soaked out from the blood is restored to the circulation. A smaller duct drains off portions of the right side of the trunk into a right branch of the superior vena cava (Fig. 58, 7i), and at vari- ous other points in the body lymphatics empty into blood vessels. Throughout the course of the lymphatics are found valves much like those in the veins (Fig. 59). These prevent the FIG. 58. -The Thoracic Duct. lymph from taking a a,b = thoracic duct. backward course. Small c = opening of duct into veins. swellings (lymphatic d— lymphatic nodes in lumbar re- 7 N •,••> ~ -, gion. nodes) are likewise found f, g, h = superior vena cava and its at frequent intervals branches. /T7,. ~~x mi 1 = part of rib. (Flg- 59); Their Prmcl' pal function is supposed to be that of forming new white corpuscles. They also A STUDY OF THE CIRCULATION OF BLOOD 151 probably serve as filters in which disease germs and other foreign bodies are removed from the lymph and destroyed. The Lacteals. — One portion of the lymphatic system has been already referred to in our study of the villi of the small intestines (see p. 95). The lacteals were described as small tubes in the center of each villus (Fig. 35). They are, however, larger than the lymphatic in other parts of the body. The fat which is absorbed by these lacteals is poured with the rest of the lymph into the thoracic duct, and by this indirect course reaches the blood that enters the right auricle. Unlike the other mi- FlG 59 _A Lymphatic trients, therefore, the fat does not Node, showing Lym- pass through the liver on its way to Phati?s (wjth Valves) entering and leaving the the heart. Node. 5. HYGIENE OF THE CIRCULATORY SYSTEM Effect of Heat and Cold on the Arteries. — It is a fact of common experience that, when the hands or other parts of the body are plunged into hot water, they assume a bright red color. We know, too, that when first exposed to a cold temperature, the surface of the body becomes pallid. These changes in color are due to the action of the muscles in the walls of the arteries. Heat causes the muscles to relax, .thus allowing a greater quantity of blood to flow through the tissue; cold, on the other hand, stimulates the arteries to contraction. If, however, the cold temperature is not too great, the walls of the arteries soon relax, and one feels a warm glow all over the body. These facts will be referred to again in the discussion of bathing (p. 240). 152 STUDIES IN PHYSIOLOGY Colds and their Prevention. — Prolonged exposure to cold, the wearing of wet clothing, or sudden exposure to a draught of air often results in a contraction of the arteries in the skin. The blood is thus driven away from the surface to the internal organs of the body, and a condition of conges- tion in these organs is the result. We describe this condition as a " cold." The real cause of colds is not yet fully under- stood. It is probable, however, that frequently the conges- tion of the internal organs, which may follow an exposure, favors the growth of disease producing bacteria, should these be present in the air passages or in the alimentary canal. Those who are accustomed to taking vigorous exercise followed by cold baths are less liable to colds. The wearing of woolen underclothing is another means of prevention, since this material, unlike cotton and linen, does not allow the skin to be acted upon quickly by sudden changes of temperature. It is 'without doubt unwise to keep the neck and throat muffled with furs or other wrappings ; for when they are removed the sensitive skin is more easily affected by a slight draught. Effect of Exercise on the Heart.1 — The pulse rate is slowest when we are asleep. As the activities of the day begin, the heart beat is quickened, and after violent exercise this organ may beat as often as twice to three times a second. Exercise, when properly regulated, is undoubtedly bene- ficial to every organ in the body; for a higher pulse rate means that the blood is renewed in each tissue so much the oftener, that more oxygen is received from the lungs, and that more waste matters are excreted. Heart muscle itself, as well as other organs, profits by this increased activity. Effect of Exercise on the Size of the Blood Vessels. — When one is using one's muscles, greater metabolism of the tissues goes on, and a larger amount of blood is needed to supply material for repairing the waste. The sympathetic nervous system therefore causes the muscular walls of the arteries to 1 See " Laboratory Exercises," No. 29. A STUDY OF THE CIRCULATION OF BLOOD 153 relax in the organs that are active. It is manifestly impos- sible to have an increased supply of blood in the organs of digestion in the muscles, and in the brain all at the same time. This is the reason why it is unhygienic for an adult to exercise violently or to carry on any considerable degree of mental activity immediately after eating. Persistence in violating this rule usually results in attacks of indigestion. An important advantage of proper methods of exercise comes from the fact that the blood is thus pushed onward through the veins and the lymph through the lymphatics. Most of the effect of the pulse beat is lost before the blood reaches the capillaries, and much of the force exerted on the veins and the lymphatics comes from the pressure of the overlying muscles. The valves in these tubes prevent a back- ward flow. Hence the blood and lymph are constantly pushed on toward the heart by the muscular pressure upon the veins and lymphatics, a pressure which is increased by exercise. Treatment of Cuts and Bruises. — One can tell when an artery has been cut by the fact that blood comes out in spurts. Since the blood is on its way from the heart, the flow can be stopped or lessened in this kind of accident by applying pressure on the side of the wound nearest the heart. Thus if the finger is cut deeply and the blood jets forth, a strong cord or a handkerchief should be tied loosely about the wrist, and a pencil or piece of wood should be placed beneath, and then the bandage should be twisted until the blood flow is stopped by the pressure. When blood flows evenly from a wound, it is an indication that a vein has been cut, and the pressure should be applied in a similar way on the side away from the heart. Bleeding from the nose can usually be stopped by hold- ing the head erect, and by applying cold water to the bridge of the nose or to the back of the neck. In case of a cut or of a bruise in which the skin is broken, the wound should be cleansed as quickly as possible with 154 STUDIES IN PHYSIOLOGY corrosive sublimate, carbolic acid, or some other germ-de- stroying solution. Antiseptic tablets can be obtained at any drug store, and a solution can be made by dissolving a tablet in a pint of water. This should be kept on hand and used to wash out wounds. The injury should then be covered with cotton soaked in the poison solution and bandaged, to prevent the entrance of other germs. If this is not done, bacteria are likely to settle in the wound, and healing may be delayed or even more serious results may follow. With proper treatment a wound should show no signs of the formation of pus, should not cause pain, and should heal rapidly. Effect of Alcohol on the Organs of Circulation. — Alcohol " ex- cites the vascular system, accelerates the circulation, so that the muscles and nerves are more active, owing to the greater supply of blood. It also gives rise to a subjective feeling of warmth. In large doses, however, it paralyzes the vessels, so that they dilate, and thus much heat is given off and the temperature is lowered.1 The action of the heart also be- comes affected, the pulse becomes smaller, feebler, and more rapid." — " Text-book of Human Physiology," LANDOIS and STERLING. 6. A COMPARATIVE STUDY OF THE CIRCULATION Circulation in the Earthworm. — If we examine the upper or dorsal surface of a living earthworm, we see through the skin a tube through which the blood is driven in pulses. This is called the dorsal blood vessel. Near the anterior end of the body, five pairs of large blood vessels (a-or'tic arches) branch off from the dorsal blood vessel just mentioned, sur- round the esophagus, and connect with a large blood tube that lies beneath the alimentary canal. The aortic arches pulsate like the dorsal blood vessel, and thus help to force the blood through the body. Branches of the dorsal and i For discussion of effect of alcohol on body temperature, see p. 243. A STUDY OF THE CIRCULATION OF BLOOD 155 m — ventral blood vessels carry blood to the capillaries in all parts of the body. The earthworm, then, has no heart, and it is there- fore impossible to distinguish arteries from veins. The blood is propelled through the body by the rhythmical contraction of the muscular walls of the dorsal blood vessel and of the five aortic arches described above. It has been proved that the blood flows through the dorsal vessel from the tail toward the head end of the worm, whence it is driven down to the ventral vessel by the contraction of the aortic arches. The course of the blood back to the dorsal tube is still a matter of dispute. Circulation in the Fish. — The structure of the fish heart is relatively simple. It lies near the ventral surface and has a single auricle and a single ventricle. When the ventricle contracts, the blood is forced forward a short distance through an artery, which soon divides into a series of branches on each side of the body. By these arteries the blood passes in a dorsal direction through the gills, where it loses some wastes and receives the oxygen that is dissolved in the water. The gill arteries finally empty into the dorsal aorta, from which blood is distributed to all parts of the body. From the systemic capillaries it is brought back to the auricle by veins of very large size. Hence the two systems of circula- tion (called in man the pulmonary and systemic), instead of FIG. 60. — Circulation in the Fish. a, b = arteries to gills. c = ventricle. d— auricle. e = opening of veins into auricle. /= portal veins. g = intestine. h = vena cava. k = abdominal aorta. I = kidneys. m = aorta which sup- plies region of tail. 156 STUDIES IN PHYSIOLOGY being carried on side by side as in the higher vertebrates, are arranged, so to speak, one behind the other, or tandem, and the blood is driven successively through the gill and systemic capillaries by the contraction of a single ventricle. Circulation in the Frog. — In the frog's heart there are three chambers, namely, two auricles, and a single ventricle. The Art rtery tos/ght lung - . X/ * ar?as/^ flight lung Artery to left 'Jung and stin Artery tp left arm teftaur/c/e ' Mentric/e — -/.efttvny --Dorsa/aorto --.~Arterits to A/d/ieys Mcf/ieys FIG. 61. — Arteries in the Circulation of the Frog. left auricle, as is the case in the human heart, receives the blood that has taken up oxygen in the lungs, while to the right auricle comes the blood from the other organs of the body. Both these auricles send the blood they receive into the single ventricle, and so the oxygenated blood is mixed more or less with blood that has been deprived of oxygen during its course through the body. By a compli- cated system of valves, however, the blood that has the A STUDY OF THE CIRCULATION OF BLOOD 157 most oxygen is switched off into the arteries that go to the head; the blood supplied with a moderate amount of oxygen is forced to the stomach, intestines, and other organs in the lower part of the body; while the blood with the least oxygen is turned into the arteries that carry it to the lungs. Blood from the lungs then returns, as stated above, through pulmonary veins to the left auricle ; the rest of the blood conies back to the right auricle. Circulation in the Reptiles. — In the group of reptiles (snakes, alligators, turtles) we first find the beginnings of a four- chambered heart. But while the two auricles are entirely separated from each other, the partition between the ven- tricles is not quite complete. In spite of this fact, the pul- monary and systemic circulations are carried on without any considerable mixing of blood in the two sides of the ventricle. As in man, the right side of the heart has to do with sending the blood to the lungs for oxygen; the left side supplies the rest of the body with the oxygenated blood. Circulation in the Birds and Mammals. — All birds and all mammals (including man) have the two sides of the heart completely separated from each other. There are, there- fore, two distinct auricles, each communicating with one ventricle only. Hence, we may speak of a distinct right and left heart in all animals above the group of reptiles. Comparison of the Organs of Circulation Studied. — Reviewing the facts presented above, we see that, while in each of the animals studied there is a complete circulation of the blood, the means by which this circulation is accomplished varies greatly. In the earthworm the force that propels the blood is furnished, not by a heart, but by the contraction of the muscular walls of certain blood vessels. All vertebrates (fishes, amphibia, reptiles, birds, and mam- mals) have hearts, and this is also true of many kinds of in- vertebrates. But one has only to compare the different hearts we have described to see how much this organ may be modified in structure. Fishes have a single auricle and 158 STUDIES IN PHYSIOLOGY a single ventricle. In frogs and toads (the amphibia) we find the beginnings of a right and left heart. But while the separation of the auricles is complete, the two kinds of blood are mixed in the single ventricle. The two sides of the heart are more completely separated in the reptiles, and when we come to the birds and mammals we find that there is no means of direct communication between the right and left hearts. Hence, in the highest groups, there is a dis- tinct pulmonary and systemic circulation. In our comparative study of digestion, we noted an increas- ing complexity of structure from the earthworm, through the frog and bird, to the mammal. The same fact is evi- dent in considering the various circulatory systems. The higher animals have more complete machinery for doing the work of the body, and for this reason they can carry on the processes of life more perfectly. CHAPTER IX A STUDY OF THE SKELETON X-Ray Pictures. — One of the marvelous discoveries of the closing years of the last century was that of the so-called X-rays. If, when a sen- sitive photo- graphic plate is held in position behind a man, these electrical rays are focused upon any part of his body the hand for in- stance, a picture is produced on the plate like that shown in Fig. 62. One can see the faint out- lines of the hand, and within it a clear picture of the bony skeleton that forms its framework. The Uses of the Bony Framework of the Body. — In certain regions of the body, bones surround and protect delicate organs. The brain, for example, is inclosed within a bony box ; the eyes are set into deep sockets ; the delicate mech- 159 FIG. 62. — X-Ray Picture of the Hand. 160 STUDIES IN PHYSIOLOGY anism of the inner ear is hidden within the hardest bone of the body ; and the organs of the chest cavity are well pro- tected by the ribs and breastbone. In other parts of the body, as in the arms and legs, the skeleton is surrounded by the muscles, nerves, and other tissues. Here the bones act as levers, which are moved by the muscles whenever we wish to go from place to place, or whenever we desire to move things about us. In a word, then, the bony framework (1) gives to the body its permanent shape, (2) protects delicate organs, (3) pro- vides a leverage on which muscles may act. Regions of the Skeleton. — For convenience, the two hun- dred bones of the skeleton may be divided into three groups, namely, (1) the bones of the arms and legs, (2) the bones of the neck and trunk, and (3) the bones of the head (Fig. 63). 1. THE SKELETON OF THE AKMS AND LEGS Bones of the Arm. — The skeleton of the upper arm (see Fig. 64, B) is formed by a single long bone called the hu'me- ruSj which extends from the shoulder to the elbow. In the forearm, one can feel through the flesh two separate long bones, of about the same size, lying side by side ; the bone on the thumb side of the forearm is the ra'di-us ; on the little finger side is the ul'na. Two rows of small bones, more or less cubical in shape, are found in the wrist. These eight wrist or car'pal bones move freely upon each other, and thus give the hand a great range of movement. By pressing with the finger on the back of the hand, one can distinguish five rather long bones, and since these lie beyond or distal to the carpals they are called met-a-car'pal bones (Greek meta= beyond + karpds = wrist). The skeleton of each finger is formed of three separate bones, and in the thumb there are two bones. These fourteen bones of the digits are called pha-lan'ges (because of the arrangement of bones in succes- sive rows like the soldiers in the Greek phalanx). A STUDY OF THE SKELETON 161 NASAL SHOULDER BLADE - (SCAPULA) •--SUPERIOR MAXILLARY BONES ^"^--iNFERlOR MAXILLARY BONE SPINAL COLUMN. CERVICAL REGION. ^-(CLAVICLE) COLLAR BONE FIG. 63. — Bones of the Skeleton. 162 STUDIES IN PHYSIOLOGY Bones of the Leg. — In the upper part of the leg (see Fig. 64, A) is a single bone, the thigh bone or fe'mur. This cor- responds in position to the humerus of the arm, but it is longer and stouter than the latter ; in fact, it is the longest bone in the body. The skeleton in the calf of the leg con- sists of two bones, tib'i-a and fib'u-la, which have a position similar to that of the radius and ulna. The tibia is on the inner or great-toe side and is much larger than the slender fibula. At the kneejoint one can feel a flat piece of bone, more or less circular in outline, called the kneecap or pa-tel'la. When one extends the knee and rests the heel on the floor, the kneecap can be easily moved about over the kneejoint. There are seven tar 'sal bones in the ankle, which like the carpals have a somewhat cubical form. They are, however, larger and less movable than the eight carpal bones of the wrist. One end of the arch of the foot rests upon the heel bone, the largest of the ankle bones. The arch is completed by the other tarsal bones, and by five rather slender met-a- tar'sals (Greek meta = beyond -f tarsds = ankle). The great toe has two, and each of the other toes three phalanges, making the same number of bones in the fingers and toes. 2. THE SKELETON OF THE NECK AND TRUNK The Spinal Column. — The erect position of the adult human body is maintained by a column of bones called vertebrae (Latin vertere = to turn, so called because these bones may be turned more or less on each other). The spinal column can be felt through the skin behind the neck and down the middle of the back. In the neck region are seven bones called cer'vi-cal verte- brae (Latin cervix = neck) ; twelve dor' sal vertebrae carry the twelve pairs of ribs ; and in the loins are the five large lum'- bar vertebrae (Latin lumbus = loin) . Below the lumbar bones is a single bone called the sa'crum. When one exam- ines it, however, four ridges and four pairs of holes are A STUDY OF THE SKELETON 163 inn car = carpal or wrist bones. cl = clavicle or collar bone. fern = femur or thigh bone. Jib = fibula. hum = humerus (upper arm bone) . inn = pelvic bone. metac = metacarpal or palm bones. metat = metatarsal bones (sole of foot) . pat = patella or knee cap. phi = phalanges of fin- gers and toes. rad — radius. scap = scapula or shoul- der blade. tib = tibia. uln = ulna. FIG. 64. — Bones of Left Arm (B) and of Leg (A) together with Bones of Girdles. evident, which indicate the regions where the five sepa- rate vertebrae that are found in the sacrum of a child have grown together. Posterior to. the sacrum in a child's skele<- 164 STUDIES IN PHYSIOLOGY 11. 12 C...J FIG. 65. —Spinal Column. A = side view, showing curves. S = sacrum. B = dorsal view, showing width of vertebrae. (7 = coccyx. C. 1-7 = 7 cervical vertebrae. sp = spinous process. D. 1-12 = 12 dorsal vertebrae. tr = transverse process. L. 1-5 = 5 lumbar vertebrae. A STUDY OF THE SKELETON 165 tr ton are four bones, which in the adult become united in one. From a fancied resemblance to a cuckoo's bill, this part of the spinal column is called the coc'cyx (from Greek, meaning cuckoo). Hence, in the spinal column of a child there are thirty-three separate bones; in that of an adult, twenty-six including sacrum and coccyx. The Structure of a Vertebra. — The vertebrae are among the most irregular bones of the body. In general one may say that each consists of two parts ; namely, a mass of bone called the cen'trum or body, and a bony arch with seven irregu- lar processes. To this region of the vertebra is given the name neu'ral arch) because it helps to inclose the neural or spinal cord. The centrum is on the ventral side of the spinal column ; circular in outline, it is flat- tened above and below, and on these surfaces are pads of cartilage that allow the vertebrae, to a certain extent, to turn and bend on each other. The weight of the body is supported by the body of the vertebra. From the neural arch, as already stated, project seven processes. One of these is the spi'nous process, which can be felt in the middle of the back. It is this succession of processes that has suggested the name spinal column. Two lateral processes extend from the side of the neural arch, and to these processes the ribs are attached in the dorsal region of the spinal column. The other four projections from the arch of the vertebra are called ar-tic'u-lar processes ; two of them face dorsally, the other two ventrally. Since they FIG. 66. — Parts of a Vertebra. A = side view. ar = articular process. B = top view. 6 = body or centrum. n = neural ring (containing spinal cord) . sp = spinous process. tr — transverse process. 166 STUDIES IN PHYSIOLOGY meet corresponding processes on other vertebrse, they allow these bones to move or articulate upon each other. The Structure of Atlas and Axis. — The two top vertebrse have a peculiarly modified structure, which allows the nod- ding and turning movements of the head. The skull rests upon the first cervical vertebra ; it is called the atlas (Fig. 67, a). This name was sug- gested by one of the myths of ancient history, in which the hero Atlas is said to have supported the world on his shoulders. When we nod, in saying "yes," the skull rocks backward and forward on the atlas. In signifying "no," on the other hand, the atlas turns about a projecting peg (Fig. 67, c) on the top of the second vertebra (Fig. 67, &). Hence, the second cervical vertebra is called the axis. When the head is tilted from side to side, the motion involves several of the cervical vertebrse. Adaptations shown in the Spinal Column. — The human spinal column is a wonderful piece of mechanism, which by its structure is adapted to perform at the same time three distinct functions. In the first place, we have seen that the bodies of the vertebrce, piled one on the other, form a column strong enough to support the weight of the body. In the neck region the vertebrse are relatively small (Fig. 65) ; but through the dorsal region their size increases, until in the last lumbar vertebra we find the largest centrum in the series. The spinal column, therefore, forms a cone with the base made by the five sacral bones united into one ; to this solid base the legs are attached. Again, the structure of the spinal column shows marvel- FIG. 67. — Atlas and Axis Vertebrse. « = atlas, on which rests the skull. b = axis, about which atlas turns, c = peg of axis projecting upward through hole in atlas. A STUDY OF THE SKELETON 167 ous provisions for securing elasticity and freedom of motion. Elasticity is secured by a succession of four curves which are best seen in a side view of the body (Fig. 65, A). By means of these curves the head and the upper part of the trunk are saved from sudden shocks that would result from running or jumping, for the curves act like a series of springs. The cartilage pads, likewise, serve as cushions to prevent jar- ring. That a consider- able range of movement is allowed by the struc- ture of the vertebral col- umn will be evident after a trial by each student. With the heels together, and the hips held firm, one can bend the body forward and backward, and from side to side; and the whole pile of bones can also be twisted around sufficiently to al- low one to look behind FIG. 68. —Spinal Column, Ribs, and Ster- num. a-b = spinal column. c= breastbone (sternum). d = cartilage of true rib. e = united cartilages of false ribs. 1-7 = true ribs with distinct cartilages. 8-10 = false ribs, cartilages united. 11-12 = floating ribs. oneself. A third adaptation that is evident in the structure of the spinal column is the protection it affords for the delicate spinal cord. The series of neural arches and vertebral bodies form a more or less continuous tube, within which lies the spinal cord. Connected with this part of our nervous system are thirty-one pairs of spinal nerves, which pass out from the sides of the tube in which the cord lies by holes between 168 STUDIES IN PHYSIOLOGY each two vertebrae. For this reason the perforations are called in-ter-ver'te-bral fo-ram'i-na (Latin inter = between -|- vertebrce = vertebrae -{-foramina = holes). One would search far before finding a more perfect means of securing strength, elasticity, and flexibility than that pro- vided in the structure of the human spinal column. The Ribs and Sternum . — Attached to the transverse pro- cesses of each of the twelve dorsal vertebrae, is a pair of slender, curved bones called the ribs. The first seven pairs bend around the sides of the chest cav- ity and are at- tached by means of cartilage to the dagger-shaped breastbone or ster'num. The cartilages of the eighth, ninth, and tenth pairs are joined on each side into one, and this is attached to the cartilage of the seventh pair. The eleventh and twelfth pairs are called floating ribs because they have no connection with the breastbone (see Fig. 68). The ends of these ribs can easily be felt through the body wall on either side of the trunk. The Pectoral Girdle. — We began our study of the skeleton by a consideration of the bones of the arm. We are now to FIG. 69. — Attachment of Ribs. 6 = body of dorsal vertebra. c = cartilage connecting rib to breastbone r=rib. st = sternum or breastbone. tr = transverse process of vertebra. A STUDY OF THE SKELETON 169 see how the arm is attached to the rest of the skeleton. Ly- ing outside the ribs at the anterior end of the trunk are two flat, triangular shoulder blades (each called a scap'u-la) (Fig. 64, scap) and two slender collar bones (each called a clavicle) (Fig. 64, cf). The /-shaped collar bones are attached ven- trally to the breastbone, while the other end of each is joined to one of the shoulder blades. In this way an incom- 5LV ,M disc is FIG. 70. — Bones of the Pelvic Girdle (Ventral View). acet = socket of pelvic bone into which fits head of femur, cocc = coccyx. disc — cartilage disk between vertebrae. il, is, pu = parts of pelvic bone. sac = sacrum. 5LV= fifth lumbar vertebra. plete circle of bones is formed to which is given the name pec'to-ral girdle (Latin pectoralis, referring to the chest). A shallow socket is found on the outside of each shoulder blade, and into this fits the proximal end of a humerus bone. It will be seen that the pectoral girdle is directly attached to the rest of the skeleton only by the ventral ends of the collar bones. Great freedom of motion for the arms is therefore possible, since the girdle itself is movable. 170 STUDIES IN PHYSIOLOGY The Pelvic Girdle. — A complete girdle of bones is formed at the posterior end of the trunk by the two pelvic bones which are attached dorsally to the sacrum and which meet in front. The upper edge of these bones can be felt at the hips (Fig. TO, 'if). On the outer side of each pelvic bone is a deep socket (Fig. 70, acet) into which fits the proximal end of the femur. Since the pelvic girdle is not movable like the pectoral, the body has a firm base Of support. The range of movement of the leg, however, is relatively small in comparison with that of the arm. 3. THE SKELETON OP THE HEAD Two groups of bones may be distinguished in the skull or skeleton of the head, namely, the bones forming the cranium which surrounds and protects the brain, and the bones that form the skeleton of the face. The Bones of the Cranium. — The cranium is a more or less spherical box, composed of eight bones as follows: The fron'tal (Latin frons, frontis = forehead) forms the forehead and the top of the eye sockets. A pair of pa-ri'e-tal bones (Latin paries, parietis = a wall) make up the principal part of the side walls of the cranium and meet along the top of the skull. On each side below the parietals, lies one of the tem'- po-ral bones. The temporal bones contain the cavities in which lie the most delicate parts of the ear. The oc-cip'i-tal (Latin ob = against + caput = head) forms the posterior part of the dorsal region of the brain box. In this bone is a large opening, the fo-ra'men magnum (Latin magnum = great + foramen — hole), through which the spinal cord passes to connect with the brain. The sphe'noid is a very irregular bone shaped more or less like a butterfly; this with the eth'moid makes a floor for the cranium, and in front toward the ventral surface separates the brain from the nose cavity. The brain is therefore inclosed by two pairs of bones (the parietals and temporals) and by four A STUDY OF THE SKELETON 173 single bones (the frontal, occipital, sphenoid, and ethmoid). In addition to these eight, there are within the temporal bones three very small bones in the middle region of each ear cavity (see p. 309). The Bones of the Face. — Twelve of the fourteen face bones are in pairs. The two cheek bones or malar bones lie on the outer and lower sides of the eye sockets. The bridge of the FIG. 71. — Bones of Skull. nose is made by the pair of na'sal bones. Between the two halves of the nose is a single thin partition of bone (the vo'mer), and on the outer walls of each nostril chamber are the tur'bi-nate or spongy bones (see Fig. 133). A small, thin tear bone on each side helps to form the separation between the eye socket and the nose, while the two paVate bones lie horizontally between the nose and mouth cavities. And, finally, there are two halves to the upper jawbone to which are united the upper teeth, and a single lower jawbone or man'di-ble in which the lower teeth are imbedded. The 172 STUDIES IN PHYSIOLOGY mandible is the only movable bone of the skull. All the others are united by irregular, toothlike processes (called su'tures) which fit closely into each other, like the dovetail joint of the carpenter (see Fig. 71.) Adaptations shown in the Structure of the Skull. — By its rounded contour, the skull furnishes the best possible protec- tion for the brain. In the first place, if a blow strikes upon the head, it would be much more likely to glance off than would be the case if the sides and top were flat. Again, the arched form of the skull, like the arch of a bridge, gives the greatest possible strength in a given amount of material to resist the force of a hard blow. Since the end of the nose and the outside ear are the most exposed portions of the head, they would, if made of bone, be in constant danger of getting broken. Cartilage, however, gives them sufficient permanence of form, and at the same time this elastic material, if bent out of shape, at once returns to its original position as soon as the pressure is removed. The deep eye sockets, surrounded by frontal, upper jaw, and cheek bones, seldom allow any blow to injure the eye. The drum of the ear, the three tiny bones of the middle ear, and the delicate mechanism of the inner ear are all buried deep in the lower part of the temporal bone which is the hardest part of the bony skeleton, and so these are out of danger. 4. DIFFERENCES BETWEEN THE SKELETON OF A CHILD AND THAT OF AN ADULT Difference in Composition. — It should be noted, in the first place, that most of the bones of the skeleton are first formed wholly of cartilage, and that this cartilage is gradually re- placed by bone through the supply of mineral matters fur- nished by the blood. This explains the fact that the bones of young children are easily bent without being broken, while those of an old person are brittle and break easily. Because A STUDY OF THE SKELETON 173 cl of this fact, young children should not be urged to walk at too early an age, lest they become bow-legged. Differences in the Skull. — In the top of a very young child's head is a space between the frontal and parietal bones, called the fon-ta-nelle'. This opening gradually lessens in size by the growth of the surrounding bones until at the end of the first or second year it is completely closed. Differences in the Spinal Column. — We have already noted the union that takes place in the five bones of the sacrum and in the four bones of the coccyx. These consolidations are usu- ally completed during the period from the eighteenth to the thirtieth year of life. Differences in the Breastbone. — In dis- cussing the breastbone, we compared with its shape that of a dagger. This bone also in childhood is formed of several distinct parts. The four pieces that make up the blade of the dagger are usually united by the twenty-fifth year, but a succession of ridges remain which show the lines of union (see Fig. 72). The handle and the point of the dagger often remain as distinct pieces until old age. Differences in the Bones of Ann and of Leg. — At the proximal end of the ulna is a projection of bone (commonly known as the "funny bone") which is readily felt at the elbow. Throughout early life this bone is separate from the ulna and hence it corresponds to the position of the kneecap in the leg. It becomes united with the ulna at about the sixteenth FIG. 72. — Sternum viewed from Front. cl = places of attach- ment of collar bones (clavicles). x = lower projecting end. 1-7 = places of attach- ment of first seven ribs. 174 STUDIES IN PHYSIOLOGY In the wrist we counted eight carpal bones, and in the ankle seven tarsal bones. During childhood, however, the heel bone consists of two separate bones ; hence until about the fourteenth year both wrist and ankle have eight separate bones. 5. STRUCTURE OF BONES l In the skeleton of vertebrates there are two different types of bone structure. One type can be studied to good advantage from a soup bone ; the other is well shown in a rib of lamb or beef. Since the latter is the simpler, it will be discussed first. Structure of a Rib. — After the meat or muscle has been removed from a lamb chop, there remains a slender, curving bone, flattened in form, which is the rib. A piece of vertebra often remains con- nected with the thicker end (compare with Fig. 69). When the rib is carefully separated from the vertebra, the two sur- faces that move on each other are found to be covered with smooth, bluish-white cartilage ; this lessens friction. If the point of a penknife be pushed into the side of the rib, a thin membrane of tough connective tissue can be raised from the outside of the bone and pulled off in sheets. This is the per-i-os'te-um (Greek pen' = around -f- oste'on = bone). The periosteum is of great importance in connection with the growth of bone, since most of the new bone is formed just be- neath this layer of connective tissue, and by its agency. "Laboratory Exercises," No. 30. FIG. 73. — Long Bone (Femur). A = rounded head which fits into sock- et of hip bone. G'= shaft of bone. D, E= rough pro- cesses to which mus- cles are attached.- F = smooth sur- face of head which articulates with the tibia. A STUDY OF THE SKELETON 175 The structure of the bone itself is best seen in cross and longitudinal sections. On the outside is a layer of compact hard bone, that cannot be cut or dug out with the point of a knife. The whole interior of the rib is made up of spongy bone (compare Fig. 74, 1, 2), the spaces in the bone tissue being filled with a soft substance called red marrow. Hence, in cutting to the center of a rib, one would meet successively periosteum, hard bone, and spongy bone with its red marrow. Structure of a Soup Bone. — A soup bone is more or less cylindrical in form, with an en- largement at either end (compare with Figs. 73 and 74). The longer central portion is called the shaft, and the enlarged extremi- ties are known as the heads of the bone. The surface of each head is covered with cartilage wherever it moves upon another bone, as was the case with the rib. The rest of the head and shaft is incased in periosteum. A longitudinal section shows the internal structure to be as follows: All over the outside is found a layer of hard bone which is thick in the shaft region and relatively thin beneath the cartilage of ' the heads (compare with Fig. 74). The interior of the heads is largely composed of spongy bone. The long central cavity of the shaft is filled with fatty yellow marrow. On comparing the rib and soup bone, we see that the marrow in the former is found only in spongy bone ; in the latter it occurs in the spongy bone of the heads, and in a solid, fatty mass in the marrow cavity of the shaft. ^G. 74. — Longitu- dinal Section of Tibia. spongy bone in heads. 3 = hard bone in shaft. 4 = marrow cav- ity in shaft. 5 = layer of car- tilage in 6 = periosteum c overing outside. 7= surface of heads cov- ered with cartilage. 176 STUDIES IN PHYSIOLOGY Advantages of Hollow Bones. — In the bone structure we have just described, two advantages are combined, namely, lightness and strength. The framework of a bicycle best illustrates the principle involved, which is that the greatest possible strength and lightness are secured in a given amount of material by using hollow cyl- inders. The spongy bone within the hard outside layer strength- ens still further the bony cylin- der without adding greatly to the body weight. Blood Supply in Bones. — In the periosteum and throughout the hard and spongy bone and the marrow run numerous blood ves- sels that bring the proteid and other food materials required for the nutrition of the living bone cells. From the blood, also, these cells take out the various mineral matters needed to form the hard intercellular substance, which gives to bone its rigidity. We The branching tubes are canals £ , , * . J , , , through which run blood ves- have already noted the fact that seis. The irregular black new red corpuscles are produced spots represent the outlines of • ,1 _, TnflT.rftw nf ] FIG. 75. — A Longitudinal tion of Bone X 200. living bone cells. The white portions of the figure show Classification of the Bones of the bony intercellular sub- the Human Skeleton. — For COn- stance (compare with Fig. 8). venience, the bones of the hu- man skeleton are divided into four groups. In the first group are the long bones, the humerus, radius, ulna, femur, tibia, fibula, metacarpals, metatarsals, and the phalanges of fingers and toes. All these bones have a structure similar to that of the soup bone just described, in that they have two heads and a shaft, and a central cavity filled with yel- A STUDY OF THE SKELETON 177 ]ow marrow. Long bones are found in the limbs, where a considerable range of motion is desired. A second group includes the so-called short bones, namely, the carpals, .tarsals, and the kneecaps. Short bones are more or less cubical in form, and in structure resemble the head region of a long bone. Much of the outside surface is covered with cartilage ; within is a thin layer of hard bone ; while the central portion is composed of spongy tissue. The short bones glide over each other, and so allow, in wrist and ankle, a considerable range of motion in a great many directions. The group of flat bones includes all those that are like the rib in form and internal arrangement. They are the ribs, breastbone, collar bones, shoulder blades, hip bones, and most of the bones forming the top and sides of the cranium. Their principal function is either that of furnishing pro- tection for the brain and organs of the chest, or that of supplying a means of attachment of the arms and legs to the rest of the skeleton. In most cases flat bones have little or no movemento Finally, the irregular bones include all those that do not readily fall into the groups already enumerated. As exam- ples may be mentioned the bones of the spinal column, in- cluding sacrum and coccyx, the sphenoid, ethmoid, and the bones of the face. Some of them serve as support (verte- brae), others protect the eyes, ears, and nose, while in the case of the lower jawbone and the atlas vertebra a consider- able range of motion is possible. 6. CHEMICAL COMPOSITION OP BONE* Effect of Burning Bones. — Bones, we have found (p. 27), consist of two kinds of material : (1) the living bone cells that provide for the growth and repair of bone tissue, and (2) the hard intercellular mineral matter (see Figs. 8 and 1 See "Laboratory Exercises," No. 31. M 178 STUDIES IN PHYSIOLOGY 75). The living tissue and the fatty marrow are easily removed by placing the bone in a hot fire. As the bone burns, it gives off the familiar smell that is characteristic of proteid, and a black color appears, which demonstrates the presence of carbon. If the flame is hot enough, the carbon is oxidized, and a white, brittle substance is left, which preserves perfectly the form of the bone. The marrow cavity is, however, completely empty, and in the burned bone the porous character of the spongy tissue becomes more evident. By weighing the bone before and after the experiment, one demonstrates that one third of the weight has disap- peared ; this of course means that a third is animal matter, and the remaining two thirds mineral matter. A bone that has been burned is very brittle, and so the experiment like- wise proves that the toughness and elasticity of bone are due to the presence of animal ingredients. Action of Acid on Bones. — In our study of digestion we learned that insoluble mineral substances are dissolved by the hydrochloric acid of the gastric juice. Hence, the hard parts of bone can be removed by the action of this acid. A rib bone that has been soaked in diluted hydrochloric acid l for several days loses most of its rigidity, and while retaining its shape, becomes very elastic and flexible. To the mineral ingredients, therefore, bone owes its hardness and rigidity for supporting the weight of the body. Nutritive Ingredients found in Bones. — When pieces of large soup bones are placed in water and heated slowly (on the back of the stove) for several hours, a thick gelatinous mass is formed. This is called soup stock. It contains most of the fats, proteids, and other nutritive ingredients of bones, and with the addition of vegetables and various condiments makes a nutritious and palatable soup. Bones, therefore, should not be regarded as refuse until after this nutrition has been extracted. 1 One part acid to six parts of water. A STUDY OF THE SKELETON 179 caps 7. A STUDY OF JOINTS Definition of a Joint. — Thus far we have considered the bones of the skeleton as though they were independent of each other. In the living body, however, we know that they are firmly attached to one another, and that thus a strong but movable framework is formed. Any region in the skeleton where motion is possible between two bones is catted a joint. Structure of a Leg Joint of Lamb.1 — Certain tissues are always present in a joint, and most of them can be easily seen in a leg joint of lamb or veal. In the first place, it is clear that in the formation of a joint there must be at least two sepa- FlQ rate bones (compare with Fig. 76). We find in the leg joint which we are study- ing that the bones are bound tightly to one another by tough bands of connec- tive tissue called lig'a-ments (Latin ligare = to bind), and that motion is possible in only two directions, like the movement of a door on a hinge. When we studied the structure of a long bone, we found a layer of cartilage covering the heads where- ever any motion upon another bone took place, and on 1 See "Laboratory Exercises," No. 35. fil- Section of Kneejoint. cartilage on end of tibia, connective tissue forming a capsule about joint. e = tendon of extensor muscle. fern = section of femur. Jib = fibula. I = ligaments between femur and tibia. pat = section of patella (kneecap). tib = tibia in calf of leg. c caps 180 STUDIES IN PHYSIOLOGY cutting away the ligaments of this joint we see the smooth surfaces of cartilage. Bet ween' them is a slimy liquid some- thing like the raw white of egg. This is the syn-o'vi-al fluid, which is secreted by the synovial membranes, that cover the inner surfaces of the ligaments, and it serves to lubricate the heads of the bones, and to prevent friction. In its appearance and chemical composition, the synovial liquid resembles more or less closely the blood serum, from which it is prepared by the synovial membrane. Besides the liga- ments which join the bones, one sees other cords of con- nective tissue called ten'dons. A tendon is attached at one end to a bone, and at the other end it becomes continuous with masses of mus- cle. By this means the pull of the mus- cle causes the move- ment of the bone. The tissues we have enumerated are present in the struc- ture of each joint in the human body. A joint, then, must have (1) at least two separate bones, (2) layers of cartilage, (3) ligaments, (4) synovial membranes secreting synovial fluid, (5) muscles and tendons. Classification of Joints.1 — The joints in the human body may be divided into four classes, which are as follows: (1) ball-and-socket, (2) hinge, (3) gliding, (4) pivot. A ball-and-socket joint, as the name implies, is formed be- i See " Laboratory Exercises," No. 36. FIG. 77. — Connective Tissue Fibers. a = small bundles of fibers. b = larger bundles of fibers. c = single elastic fibers. A STUDY OF THE SKELETON 181 tween the more or less spherical head of a long bone and a cup-shaped cavity in another bone. The best examples of this sort of joint are found at the shoulder and at the hip. Great freedom of movement is possible in a ball-and-socket joint. The arm can be moved upon the shoulder blade (1) backward and forward in a quarter circle at the side of the body, i.e. flexed and extended, (2) outward or inward in a circle in front (ab-duct'ed and ad-duct- ed), (3) the whole arm when held stiff may be made to describe a cone (cir'cum- duct'ed), and (4) it may be twisted in the socket (ro'ta-ted). A much greater range of movement than that just de- scribed is made possible for the arm by the fact that the bones of the pectoral girdle are loosely attached to the rest of the skeleton, and hence can move with the arms. The hip joint allows all four of the movements enumerated above, but the amount of motion is less, since the hip socket is much deeper, and since the pelvic bones are closely at- tached to the sacrum. Other ball-and-socket joints are found between the metacarpals and phalanges of the hand and between the metatarsals and phalanges of the foot. We have become familiar with the structure of a hinge joint in our study of the leg of a sheep. Motion is possible in but two directions. When the joint is moved so that the two bones form an angle with each other, the joint is said to be flexed; if the bones are made to form a straight line, the joint is extended. Following is a list of the hinge joints of the body: — • REGION OF JOINT JOINT OCCURS BETWEEN elbow humerus and ulna -f- radius, wrist carpals and metacarpals. fingers the different phalanges, knee femur and tibia, ankle tibia -f- fibula and tarsals. toes the different phalanges, head * lower jaw and temporal, neck skull and atlas. i This joint also belongs to the class of gliding joints. 182 STUDIES IN PHYSIOLOGY The third class includes the gliding joints, and these are usually formed of short bones. They glide over each other in several directions and so allow a small range of move- ment in many directions. KBGION OF JOINT JOINT OCCURS BETWEEN wrist radius and carpals. wrist the different carpals. knee kneecap and the femur, arch of foot the different tarsals and tlie metatarsals. head (both hinge and lower jaw and temporal. gliding) spinal column the different vertebrae, chest region vertebrae and ribs. In SL pivot joint one bone moves around a projection of the other, the latter serving as a pivot. Such a joint is formed between the first two vertebrae (see Fig. 67). The peg of the axis, projecting upward through a hole in the atlas, is the pivot about which the atlas 'turns. A rather more com- plicated kind of pivot joint is formed between the radius and a lower process of the humerus. The action of this joint is easily demonstrated in the following manner: Extend the forearm and the hand on the table with the palm up ; then, without lifting the elbow from the table, turn the hand over, so the palm is downward. In this movement the lower (distal) end of the radius crosses the ulna, carry- ing the hand along with it (see Fig. 78). It is because of this rotating motion that the radius bone has received its name. 8. THE HYGIENE OF THE SKELETON Food and the Skeleton. — In the composition of bones, we found two kinds of matter, namely, animal and mineral. For the growth of bones, therefore, it is essential that there be a supply of both of these building materials. Bone cells, A STUDY OF THE SKELETON 183 like all other protoplasm, require proteid and water; the fats and carbohydrates of food are probably converted into fatty marrow; while the intercellular substance is formed from the mineral matters brought by the blood. Milk is a most important article of diet in early life, since in addition to the other nutrients, it supplies the phosphate of lime needed for bone manufacture. In the process of refining wheat flour much of the mineral matter is lost; for this reason whole wheat flour and the coarser cereals like corn, rye, and oats are much more valuable as bone builders, and are espe- cially needful during the period of growth. The insoluble min- eral matters in these foods are made soluble by the gastric juice in the stomach. The soluble salts are then supplied by the blood to the bone cells, and these in turn convert this mineral matter into the hard intercellular substance. Effect of Pressure on Bones. — Tight-fitting clothing is a most important factor in modifying permanently the shape and po- sition of bones. Normal growth cannot be attained if the skeleton is subjected to pressure. Yet this important principle of hygiene is constantly violated by women who wear tight-fitting clothing about the waist. Baneful fashion is often followed even in youth, when the skeleton yields readily to pressure. The result is that the ribs are perma- FIG. 78. — Pivot Joint of Right Arm. A = position of bones when back of hand is down. B = position of bones when palm of hand is down. H= humerus. R = radius. U = ulna. 184 STUDIES IN PHYSIOLOGY nently bent inward toward 'the breastbone, thus interfering seriously with the action of the abdominal organs. High- heeled shoes are another frequent cause of deformity. They reduce the spring in the arch of the foot and throw too much of the weight of the body upon the tips of the toes. Shoes with narrow toes should never be worn. FIG. 79. —Effect of Tight Lacing on the Organs of Chest and Abdomen. A = normal position of organs. B = position of organs after lacing. 9. ACCIDENTS TO THE SKELETON Fractures. — Any sudden strain or blow upon a bone is liable to cause a break or & fracture, especially in later life, when the bones are brittle. If the bone is broken into but two pieces, the accident is described as a simple fracture ; when several breaks occur, it is called a splintered fracture ; and if the pieces of bone work out into or through the flesh, a compound fracture results. Fractures occur more com- monly in the shafts of long bones, and they can usually be recognized by the fact that an extra joint is thus formed and by the fact that the broken ends grate against each other. In treating a fracture, the pieces of bone must be brought A STUDY OF THE SKELETON 185 back into position (this is called " setting " the bone), and must be held in place by splints until the ends have become firmly "knit" together. Unless it is impossible to secure surgical assistance within a day or two, the setting of a bone should never be attempted by one who is not familiar with the skeleton. In general but two rules should be fol- lowed in case of a fracture : ftrst, send for a doctor; second, keep the broken bone perfectly quiet in as comfortable a posi- tion as possible. Cold water applications often reduce the pain and prevent inflammation. Movement at the point of fracture almost always causes inflammation, which makes the setting difficult ; and if moved suddenly, a simple break may become a compound fracture. Dislocations. — A dislocation is an accident to a joint in which the ends of the bones are forced apart. One can usually recognize a dislocation by the unwonted protrusion of the bones, and by the pain caused when any motion at the joint is attempted. Since the ligaments bind the bones to- gether rather closely, a dislocation often results in a wrench- ing or tearing of the connective tissue about a joint ; swelling and discoloration follow quickly ; and it is therefore neces- sary to put the bones back into place, or, in other words, to "reduce the dislocation" as soon as possible. If .surgical aid can be procured, it is better to apply cold water to the joint and wait for the doctor's arrival, since by unskillful treatment further injury to the joint may result. When skilled treatment is impossible, most dislocations can be reduced by steadily pulling the bones apart until it is possi- ble for the ends to glide back into place. Sprains. — When a sudden strain causes neither a fracture nor a dislocation, it often gives rise to a twisting or tearing of ligaments and tendons in the region of a joint. Such an accident is called a sprain. The injured region is usually swollen and painful. Since it is difficult to distinguish a sprain from other accidents to the skeleton, medical assist- ance should be summoned and the following directions care- 186 STUDIES IN PHYSIOLOGY fully followed : (1) the sprained member should be placed at once into cold water or into hot water and held there for some time ; (2) it should meanwhile be rubbed as vigorously as possible without causing pain ; (3) arnica, Pond's extract, or some other " pain killer " should be applied ; (4) the sprain should then be bound in a tight bandage (these four applications tend to keep down the swelling) ; and (5) (most important of all) the joint should have complete rest until all swelling and soreness have disappeared. It is probable that more permanent injuries result from careless treatment of sprains than from all other accidents to the skeleton. 10. A COMPARATIVE STUDY OF SKELETONS1 Skeletons of Invertebrates and of Vertebrates. — We have defined a vertebrate as an animal with a backbone, and an FIG. 80. —Living Coral surrounded by its Outer Skeleton. invertebrate as an animal without a backbone. This dis- tinction between the two subdivisions of the animal king- dom can be carried still farther, and we may say that in general the invertebrates either have no skeleton at all or that, when present, the skeleton is on the outside of the 1 See "Laboratory Exercises," No. 37. A STUDY OF THE SKELETON 187 body; whereas vertebrates are characterized by the pos- session of a bony skeleton within the body. There are, however, exceptions to this general rule. Invertebrate Skeletons. — Most of us are familiar with com- mon coral in its branching form or in the spherical form which resembles the human brain (Fig. 80). This coral is really a skel- eton formed by coral animals as a means of protection. The depressions in the surface of the1 skeleton in- dicate the posi- tion and form of the bodies of the animals. Starfishes, too, construct a cov- ering of bony plates in the skin which, al- though hard FIG. 81.— Living Starfish, showing Tube Feet pro- ' jecting from the Lower Surface of the Skeleton. can be moved The Mouth is in the Center of the Star, by the living animals (Fig. 81). The outside skeleton of the mollusks (snails and clams) takes the form of a single or double shell, within which the animal can withdraw itself, and oftentimes completely close the shell. On the exterior of the body of lobsters, crayfishes, and of most insects is a hard covering that incloses the soft parts. As the animal grows, the shell becomes too small, and then it is split along the dorsal surface. The animal then pulls its body out of the shell and withdraws to a protected place until a new hard skeleton is formed. One might compare 188 STUDIES IN PHYSIOLOGY this means of protection of these crus-ta'cea (Latin crusta = the hard surface of a body), to that afforded by a coat of mail worn by the warriors of the middle ages. This com- parison is more striking since some of the plates of this outside skeleton move over each other at the joints in a manner similar to the iron plates of the armor (Fig. 82). Vertebrate Skeletons. — It would be impossible to give in a limited space any extended account of the skeletons of the FIG. 82. — The Crayfish, showing Hard Exo-skeleton. various groups of vertebrates. A few facts may be noted, however. We have learned that the skeleton of a young child is first formed of cartilage; some of the fishes (sharks and sturgeon) possess a cartilaginous skeleton throughout life. In all of the vertebrates, with the exception of the snakes (and a few rare lizards and amphibia), we find anterior ap- pendages that correspond to the arms of man, and posterior appendages corresponding to legs. Both sets of these appendages are used by fishes in swimming; the posterior limbs of a frog are employed in jumping and swimming; while in birds the anterior appendages are of use in flying. A STUDY OF THE SKELETON 189 In spite of these great differences in form and function, we find in each appendage bones that correspond to some or all of those in the human arm and leg (compare Fig. 83). Frogs have a breastbone, but no well-defined ribs ; snakes have ribs the whole length of the body (sometimes several FIG. 83. — Skeleton of the Frog. Carp = carpal bones (6) . II, Pit = pelvic girdle. R, U = radio-ulna. Cor, Cl, Sc = pectoral girdle. Fe = femur. Tarsi, Tibl, Fiblr = tarsal bones (5). Ti + Fi = tibio-fibula. F1 = first vertebra. FK = ninth vetebra. /' = rudiment of sixth toe. I, II, III, IV, V = metacarpals and metatarsals. hundred pairs), but have no breastbone. In addition to their inside skeleton, turtles have thick shells which are on the outside like the skeleton of an invertebrate (see p. 245). In birds most of the bones are hollow and filled with air, an arrangement that helps to give to these animals some of their buoyancy in flying. 190 STUDIES IN PHYSIOLOGY ~£one Anterior Appendages of Mammals. — In the single group of mammals we find most striking variations in the form and functions of anterior appendages. One would expect to find little in common in the structure of a bat's wing, a seal's fin, a giraffe's front leg, and a lion's paw. Yet in all these appendages there is a single humerus, a radius, an ulna, and a number of carpals, metacarpals, and phalanges. Equally interesting is a. comparison of the use made by mammals of the digits or fingers of the anterior limb. Bears walk on the palm of the hand and hence are called flat-footed. Elephants rest their weight on the under surface of four of the five digits. The rhinoceros FIG. 84. — Sectional View of Foot of Horse. Cranium Azit -^•-Cervical Vertebra* ( 7) Carpal JUeto&trjMl Banes FIG. 85. — Skeleton of the Horse. has three fingers or three toes on each appendage. In cows, deer, and sheep we find but two fingers on each front foot, A STUDY OF THE SKELETON 191 on the tips of which the weight of the body is supported. Finally, horses have but a single digit on each foot, the end bone of which is covered with the hoof (Fig. 84). The story of the horse, as it is learned from the fossil bones obtained from the rocks, is an in- teresting one. The earliest horse of which we know any- thing was about the size of a fox, and walked on the dis- tal part of four fin- gers of each front foot and of three hind toes, all of about equal size. Gradually, how- ever, the descend- ants of this animal came to walk more and more on the tips of the middle fingers and the mid- dle toes. The little fingers were there- fore too short to touch ground, they became smaller as the ages passed, and have altogether dis- Fore Foot Hind Foot S One Toe , 3 7 One Toe Splints of 2-^nd 4*d\$ts < Splints of •j 2"J8nd 4*di£f» % S Three Toes Three Toes 5ide toes Side toes nottouchingtheground not touching the ground f Three Toes Side toes touching the ground; splint of 5* digit J ) Three Toes Side toes touching the ground u U Four Toes fFour Toes H Three Toes ill Splint of 5&di$t. Splint of 1'-' digit FIG. 86. — The Development of the Fore and Hind Feet of a Horse. Feet of Modern Horse are figured at the Top. — From diagram in American Museum of Natural History. appeared in the modern horse. As the middle digit came to be used more, its size notably increased, while there was a corresponding decrease in the size of the digits on either side. In skeletons of horses that lived nearer modern times, we lose all trace of the phalanges of these two side digits, and in the 192 STUDIES IN PHYSIOLOGY horse of to-day there is nothing to suggest this long story with the exception of two so-called splint bones along the sides of the lower leg ; these are the remains of the two meta- carpal bones to which the two side fingers were attached. Peculiarities of the Human Skeleton. — In the human body there is no bone or set of bones that is not found in varied form in all the mammals and in most other vertebrates; indeed so far as we can learn from the structure of his skele- ton, man is much more closely .related to the gorilla and the chimpanzee than are these animals to the lower monkeys. Yet there are certain general peculiarities of form that are found in the skeleton of man alone, these distinctive charac- teristics being due in a great degree to his erect position. In the first place, in even the highest monkeys the length of the arms is nearly equal to that of the legs. For while the gorilla can walk on two feet, all four appendages are often employed in locomotion. In man, on the other hand, the legs are much longer than the arms, an advantage that permits of long strides in walking. Again, no other animal has the four curves in the spinal column and the arched instep. These provisions are more necessary in man because the head rests on the top of the spinal column, and any sudden jar would be transmitted to the brain were it not for the presence of these elastic springs. The human skull is nearly balanced on the top of the spinal column, while that of other animals is attached to the anterior end of a more or less horizontal backbone. Man's cranium is much larger than the skeleton of the face, whereas even in the highest monkeys the heavy face bones more than balance the bones of the brain-case, and thus it is difficult for the animal to hold its head erect for any length of time. Finally, the gradual increase in the size of the vertebrae from the neck to the sacrum and the breadth of the pelvis (both characteristics peculiarly human) give a stable base on which the erect trunk is supported by the legs. CHAPTER X A STUDY OF THE MUSCLES Importance of Muscle Tissue. — Muscle tissue constitutes or almost half of the weight of the human body. In this kind of tissue is found one fourth of all the blood. But the importance of muscle tissue is appre- ciated, even more fully, when we realize that nearly every kind of movement in the body is due to the action of the muscles. Not only do they bring about the more obvious motions of the arms, the legs, the trunk, and the head, but also to muscular action are due all the contractions of the heart, of the stomach, and of the other internal organs. Every change in the expres- sion of the face, and every variation in the tone of the voice is likewise a result of Fia.ST.-Musdes^of the Head and the action of this all-important tissue. Hence we are not surprised that there are over jive hundred separate muscles, which vary in length from the fraction of an inch (within the ear cavity) to over a foot and a half (down the front of the thigh). Kinds of Muscle. — All of these muscles are in one way or another under the control of the nervous system. Some o 193 194 STUDIES IN PHYSIOLOGY of them are directed by the conscious portions of our brain. Thus we can close our fingers and open them as we please ; we can move the eyes, the head, and the legs at will. We call all the muscles that are controlled by our will power, vol'un-ta-ry muscles (Latin voluntas = will). Most of the muscles of the throat, those of the gullet, stomach, and intestines, on the other hand, act without any voluntary direction on our part, and they are therefore called in-voV- un-ta-ry. 1. THE VOLUNTARY MUSCLES * The Biceps Muscle. — When I place my left hand on the front surface of my right upper arm, and then draw up my right forearm as far as possible, I feel the muscle in front of the humerus become shorter, thicker, and harder. By extending the forearm again, a tough cord or ten1 don can be felt at the lower or distal end of the muscle. This tendon attaches the muscle to the radius bone. The proximal end of this muscle is covered by thick layers of flesh, but if these were removed, we should find two other tendons, which connect the muscle with pro- jections on the shoulder blade (Fig. 88). We are now pre- pared for certain definitions. The muscle we have been studying is called the bi'ceps, from the fact that its upper iSee "Laboratory Exercises," No. 33. FIG. 88. — Action of the Biceps Muscle. a = attachment of tendons to shoulder. _?* = elbow point. P = attachment of lower tendon to the radius. W = weight of the hand. A STUDY OF THE MUSCLES 195 end has two heads or tendons (Latin U = two -f caput = head). The central portion or the part that contracts is called the belly of the muscle. Since the biceps muscle is joined above to the shoulder blade and below to the radius, it therefore passes across two joints. When we lift a book with our forearm, the upper tendons remain practically unmoved ; this end of the muscle is then called its origin. The tendon attached to the radius, however, is made to move considerably, and to this end is given the name insertion of the muscle. If, on the other hand, we climb a rope hand over hand, the elbow joint is held firm, and the motion takes place at the shoul- der. Under these conditions the radius end is the origin, and the scapular end the insertion. By origin of a muscle is meant the end that moves least; by insertion, the end that moves most. In the majority of muscles one end is always origin, the other insertion. The Triceps Muscle. — If we straighten or extend the fore- arm as far as possible, the belly of a muscle behind the humerus is found to swell. This is the tri'ceps muscle (Latin tri = three -f- caput = head), so called because it has three tendons at its upper end. These tendons form the origin of the triceps, and are attached to the shoulder blade and to the humerus. The insertion of the muscle is on the projecting head of the ulna (commonly known as the " funny bone") (see Fig. 89). Arrangement of Muscles in the Body. — If the biceps muscle is made to contract, the forearm is brought upward or flexed. When the triceps exerts its force, the biceps relaxes and the forearm is straightened or extended. This illus- trates the paired arrangement of muscles throughout the body ; for a flexor muscle on one side of a joint is bal- anced by an extensor on the other side, which acts as its antagonist. Along the palm side of the forearm are the bellies of the flexor muscles that bend the fingers, while on the back of 196 STUDIES IN PHYSIOLOGY the radius and ulna are the ringer extensors. The origin of each of these sets of muscles is in the region of the elbow joint. Long tendons, easily felt in the wrist region, run over the carpals and metacarpals and are attached to the Extensor* of fh« H»nd ......_ _/lexot$ of the Hand Ft«»0'« Of th* Foot _G«itroenemiu» _Tendo AcriillM FIG. 89. — Muscles of the Body. tips of the various phalanges. By this arrangement the muscles that move the ringers are placed up in the forearm out of the way, thus allowing a small and graceful outline for the hand. The same pairing off of muscles is likewise seen in the leg A STUDY OF THE MUSCLES 197 region. One muscle is especially developed in the back of the calf of the leg, and is attached to the heel bone by the tendon of Achilles (so called because in Greek mythology the hero Achilles is said to have met his death by an arrow that pierced this tendon). When the extensor muscle we have been describing contracts, it raises the body on tiptoe (see Fig. 89). The corresponding flexor, that causes one to stand on the heels, runs from the knee down the front of the tibia, its insertion being on the ankle bones. In the ventral wall of the abdomen, in the region of the face, and in some other parts of the body, the muscles are arranged in broad, flattened masses and serve as a movable wall to inclose the cavities within. Like the muscles of the appendages, they are attached to the skeleton or to each other by tendons. Structure of Voluntary Muscle. — A thick piece of steak cut from a leg of beef furnishes good material for the study of voluntary muscle.1 One sees that the muscle can be separated into rather large, more or less cylindrical or prism-shaped masses, that run along the leg bone. Each of these masses is called a muscle bundle. It is surrounded by a tough, glistening sheet of con- TiPPtivp ti^np Pallprl wr FlG' ^- — Muscle Bundles (/) bound L Per~ together to make a Piece of Muscle. i-my'si-um (Greek peri = around + mys = muscle). When this perimysium is pulled off, the bundle is found to be composed of smaller bundles, and each of these is enveloped in a thin sheath of peri- mysium. These smaller bundles, in turn, can be separated still further until one gets a bundle, or piece of bundle, so small that it can hardly be seen with the naked eye. 1 See "Laboratory Exercises," No. 34. 198 STUDIES IN PHYSIOLOGY FIG. 91. — A Portion of Two Striped Muscle Fibers, highly magnified. n = nucleus. s = covering of fiber. If this bit of muscle is put on a glass slide in a drop of water, teased apart with needles, and examined with the compound microscope, it is found to be composed of tiny threads lying side by side, and held together by the thin sheet of perimysium. Each of these threads is a muscle fiber. Close examination shows that each fiber is marked by very minute lines that run across it, and give it an appearance resem- bling that of a very fine file. Because of this appearance, voluntary muscle is also called striped muscle. If the fibers are properly stained, nuclei appear here and there, showing that muscle, like all other kinds of tissue, is made up of cells. When a muscle is made to con- tract, each one of the fibers, like the whole muscle, becomes shorter, thicker, and harder. Blood Supply of Mus- cles.— Fresh muscle is deep red in color, and this is due to the pres- ence of a great quantity of blood. If one finds in the muscle the open- FlG> 92. — Blood Vessels in a Piece of ing of a large blood Striped Muscle, magnified 150 times. vessel and forces into it, 'cope' by means of a syringe, a mixture of hot gelatin stained with some coloring matter, each minute blood vessel is distended, A STUDY OF THE MUSCLES 199 and when the gelatin cools, the network of blood vessels can be traced to the fine capillaries that run around the smaller muscle bundles. A microscop- ical preparation shows still finer branches between the individual fibers. From the lymph that comes from these microscopic tubes, each muscle fiber takes the all-important proteid, the sugar, fat, and water, and to the lymph in exchange are given the waste car- bon dioxid, water, and urea pro- duced during muscular activity. Nerve Supply to Muscles. — Much of the wonderful progress in micro- scopical work that has been made in recent years, has been due to discoveries in methods of staining. Several chemical mixtures are now ?^ 1 11 known which, if applied to muscle, will stain nerve tissue in such a way that it can be readily dis- tinguished from every other kind of tissue. Hence in microscopical preparations, it is possible to trace the minute branches of a nerve from the brain or spinal cord, through the muscle bundles, to their endings on the muscle fibers. FIG. in We see, therefore, that the ner- vous system controls the action not only of a whole voluntary muscle, but also of each individual muscle fiber. Standing. — Although to most of us it seems an easy matter 93.— Muscles used standing erect. I = muscles back of calf. 1 = muscles front of calf. II = muscles back of thigh. 2 = muscles front of thigh. Ill = muscles of spine. 3 = muscles of abdominal wall. 4, 5 = muscles of front of neck. Arrows indicate direction of action of muscles. 200 STUDIES IN PHYSIOLOGY to stand erect, yet, if we stop to think of it, in this ap- parently simple process a great many muscles must act together at the same instant. That this cooperation of the muscles is due to the control exercised by nerve tissue is proved by the fact that faintness or any sudden shock to the nervous system, destroys for the time being the power of standing. Not only must the muscles of a small child be developed before it can support itself on its feet, but the brain cells and nerves also must be educated. The ten- dons of the muscles, we have found, run over the joints, and the muscles are arranged in pairs. In standing, the various joints (ankle, knee, thigh, trunk, and neck) are kept rigid by the combined pull of both extensors and flexors. Small wonder, then, that it takes a child a year or two to learn to stand, for more than a dozen sets of muscles must be taught to work harmoniously (see Fig. 93). Walking. — When standing, one makes the muscles of one's limbs contract at one and the same time. Walking, on the other hand, involves the successive action of the various flexors and extensors. If we are standing with both feet together, and put the right foot forward, the motion is accomplished by the flexor muscles in front of the hip joint. We then touch the right heel to the ground, and later the whole sole of the foot. Meanwhile the body has fallen forward so its weight comes to rest on the right leg. A forward push is given with the toes of the left foot by the contraction of the big extensor muscle at the back of the calf of the leg. Walking may, therefore, be described as a series of falls in a forward direction, in which the balance is re- stored by thrusting out the other, foot. Not only are the leg muscles used in this form of locomotion, but also many other muscles are brought into play. Thus it is easier to walk if the arms are allowed to swing. The whole body sways more or less from side to side as well as backward and forward, and this involves motion between the vertebrae. Running. — • When one is walking, one foot or the other is A STUDY OF THE MUSCLES 201 always touching the ground. In running there are instants of time when neither foot touches earth. Kunning differs from walking, too, in that the heel does not touch ground in running ; for when the foot is thrust forward, one lights upon his toes alone, and then the toes of the other foot give the body a vigorous push forward. 2. INVOLUNTARY MUSCLE Nerve Control. — We have denned involuntary muscle as tissue that contracts and relaxes without being controlled by the will power. This does not mean that the nervous system has no control over it, for, as we have already learned, its action is directed by a special mechanism in the trunk of the body called the sympathetic nerve system. •7* FIG. 94. — A Plain Muscle Fiber. / = cell body. n = nucleus. P = granular substance near the nucleus. Functions. — Involuntary muscle makes up most of the thickness of the walls of the heart, of the alimentary canal, and of the blood vessels. It is an experience common to all of us that processes, like the winking of the eyes, breath- ing, and walking, are carried on without conscious thought. We can, however, close the eyelids when we wish, breathe rapidly, slowly, or stop breathing for a time, and can con- sciously direct the leg movements in walking. These activities are, therefore, regarded as automatic, and the muscles that carry on these movements are voluntary muscles. Involuntary muscles carry on the functions that are beyond the control of the will. Structure of Involuntary Muscle. — If a piece of stomach muscle is teased apart with needles and then examined with a compound microscope, this tissue is found to consist of 202 STUDIES IN PHYSIOLOGY small sliver-shaped cells, each having a nucleus. Unlike the voluntary muscle fibers these have no cross stripes, and hence this kind of tissue is often called un- striped or plain muscle. The cells are usually joined in such a way that they form thin sheets. They are supplied with branches of blood vessels and with nerve fibers from the sympathetic nerve system. Heart Muscle. — While heart muscle is involuntary so far as its action is concerned, in its structure it presents certain peculiarities. Like other in- voluntary muscles, it consists of sepa- rate cells, each with a distinct nucleus. FIG. 95.— Two Muscle (It is impossible to distinguish the Fibers of the Heart. outlines of cell bodies in voluntary J = line of junction be- muscies.) But, on the other hand, tween two cells. ' n = nucleus. heart muscle resembles voluntary mus- p = processes which cle in its cross-striped appearance. The joined another 1,1 i ,-, « • ,1 fiber muscles that make up the wall of the heart contract more rapidly than do other involuntary muscles, but less rapidly than other cross-striped tissue. 3. THE HYGIENE OF MUSCLE Necessary Conditions for Healthy Muscles. — If one is to have 'a well-developed and healthy muscular system, four conditions must be fulfilled : the body must be supplied with nutritious food ; there must be a generous amount of fresh air ; the muscles must be exercised vigorously ; and this exer- cise must be followed by periods of rest. We will now consider in turn how each of these requirements can be met. Food. — We have learned that 75% of muscle is com- posed of water, and that proteid is the most important A STUDY OF THE MUSCLES 203 solid ingredient. Mineral matter and fats are also present in small quantities, even in the leanest of muscle. During the period of growth all these nutrients should be sup- plied for muscle building, but proteid is absolutely essen- tial. Grape sugar is also found to be an important food during muscular contraction. When training for contests the diet of athletes is carefully regulated: rare meats, coarse breads, eggs, vegetables, and fruits are supplied in generous quantities ; pastry and fats are reduced to a mini- mum. Tobacco ' and alcohol in any form, however, are absolutely prohibited. Such a diet is undoubtedly far more wholesome to develop a healthy boy or girl, man or woman, than are the rich gravies, pastries, and condiments which are found on too many tables. Fresh Air. — Healthy muscle is absolutely powerless, how- ever, unless in addition to food, it receives a supply of oxy- gen; for all muscular energy is produced by oxidation. Impure air, besides being deficient in oxygen, contains carbon dioxid and other gases that are exceedingly harmful to the tissues (see p. 221). Well-ventilated sleeping rooms are most essential for healthy living, for during the night the body gets rid of much of the waste carbon dioxid that is formed during the day. Exercise. — It seems like a contradiction to say that the only way to get more and better muscle is to destroy what we already have. Every one knows, however, that if the muscles of the arm or the leg are not used for a time, they become weak and flabby, and yet every time a muscle is made to contract, some of its substance is oxidized. New muscle must then be formed by the process of assimilation to take its place. A certain amount of vigorous exercise each day is essen- tial if one is to keep one's body in the best physical condi- tion. This amount of course varies with the individual. It should never be carried to an excess, resulting in exhaustion, but should usually be at least the equivalent of a five-mile 204 STUDIES IN PHYSIOLOGY walk or a fifteen-mile bicycle ride. Fortunate is the boy who can spend the early years of his life in the country, and who has been taught to do a certain amount of manual work each day out of doors. Regularity in exercise is as important as regularity in eating. One cannot exercise vigorously one day and expect its good effects to last for a week. We should not call upon the muscles for violent exertion immediately after rising and before breakfast, nor should we exercise until at least a half hour after eating. The physiological reasons for these directions have been already given in our study of the circulatory system (p. 153). The best forms of exercise are those that call into play the greatest number of muscles. For this reason gymnasium training is better than many kinds of outdoor sports. In the gymnasium, too, special forms of exercise can be taken to develop any muscles found to be weak. On the other hand, lawn tennis, golf, rowing and football have the additional advantage of being played in the open air, and games of this sort are usually more exhilarating than are set forms of exercise with apparatus. To secure the full effect of any kind of exercise, it should be followed by a moderately warm, then by a cold shower, or sponge bath, and by a good rubbing of the body with a coarse towel. Muscles are not the only tissues developed by exercise. Every muscular contraction is directed by some kind of stimulus from the nervous system. Before the muscles of the arm or leg contract, a " message " must come to them from the brain or spinal cord ; hence nerve tissue is likewise developed by exercise. Rest. — If physical exertion is carried beyond a certain point, exhaustion results, and the muscles cannot be made to contract until after a period of rest. Since all muscular contraction involves metabolism of tissue, periods of rest must be allowed for the muscles to get rid of their wastes and to build up new tissue in place of the old. The feeling of weariness after long-continued exercise is probably due to A STUDY OF THE MUSCLES 205 the presence in the body of great quantities of carbon dioxid, water, and urea. One can often rest to good advantage by changing from one form of activity to another, but from eight to nine hours of sound sleep each night are indispens- able for the health of a growing youth. The necessity for sleep will be further discussed in the study of the nervous system. 4. A COMPARATIVE STUDY OF LOCOMOTION Amoeba. — We have already studied the method of loco- motion of amoeba (see p. 24), and we have seen that there are certain cells in the human body (white blood corpuscles) that show a similar amoeboid movement. In all these cells the whole cell body may be said to have a power of contraction something like that seen in highly developed muscle tissue. Paramecium. — In the group of the Protozoa, or single celled animals, there is another method of locomotion which is wonderfully interesting. If one covers some hay with water and allows the mixture to stand for a few weeks, on examining a drop of this so- called hay infusion one will find a multitude of microscopical animals Fia.96.— A Paramecium. that move from one part of the slide to another with great rapidity. By c. vac. = contractile vac- uoles (probably for excretion) . adding to the water a drop of gum /. Vac = food vacuoles. arabic or other sticky solution, their motions can be retarded so that one is able to make out their form and structure. gul. = gullet. mth. = mouth-opening. Each par-a-me'- ci-um (for so this animal is called) is a single cell, shaped something like the sole of a slipper. Its whole outer surface 206 STUDIES IN PHYSIOLOGY is covered with a multitude of tiny hairlike projections which are called ciVi-a, and these wave back and forth like little oars, driving the animal through the water. In paramecium, then, the outer surface only is adapted by the cilia for loco- motion, whereas all the cell protoplasm of amoeba may be concerned in the process. Earthworm. — If one watches the locomotion of an earth- worm, one sees that the animal first pushes forward the ante- rior end and then draws up the posterior part of the body. These movements are accomplished in the following way. The outer wall of each joint or segment is composed of (1) muscle fibers that run around the body (circular muscles), and (2) those that extend from the anterior to the posterior end of the segment (longitudinal muscles). When the circu- lar muscles at the anterior end contract, the segments become smaller in diameter, but longer. If now the longi- tudinal muscles act, the joint is shortened, and in this way the segments behind it are pulled forward. In the same way the circular and longitudinal muscles in each of the hundred joints, more or less, contract successively, and thus a wavelike movement passes from the anterior to the pos- terior end of the body. The forward movement of the worm would be impossible, however, if there were not some means of anchoring the segments after they have been pushed forward. Let one grasp the tail end of a worm and draw the rest of the body across the finger tip. The scratching sensation is caused by four double rows of tiny bristles. These rows extend the whole length of the animal on its ventral surface. To the inner end of each bristle are attached small muscles by which it can be pointed either forward or backward. The bristles, therefore, not only make the ventral surface roughr but also serve as very simple appendages to assist the longitudinal and circular muscles in locomotion. Locomotion in Water. — Most vertebrates that live in the water are provided with appendages that act like paddles. A STUDY OF THE MUSCLES 207 Fishes usually have two pairs of fins that correspond in a way to the arms and legs of man. Their principal use is to steer the animal through the water, for most of the force for the forward movement is supplied by the muscles that move the tail from side to side. Such rapid movement is possible by this means of locomotion that the salmon is able to travel twenty miles an hour. Frogs in swimming use their hind legs almost wholly. All the joints are first flexed, thus doubling the appendages near the body ; they are then quickly straightened by the strong extensor muscles, and the push of the webbed feet against the water drives the body forward in a succession of jerks. Swimming and wading birds (ducks, flamingoes) are likewise provided with webbed feet. Alligators and crocodiles swim with their tails, like fishes. Locomotion in the Air. — Animals that fly require a much more highly developed muscular system than do those that swim. The water buoys up a fish and furnishes a dense medium for the fins and tail to push against. Air, on the other hand, is eight hundred times lighter than water. We have seen that the skeleton of a bird is made light by the air cavities within the bones. The skeleton of a crow weighs when dried only one three-hundredth of a pound. The wings of a bird are anterior appendages wonderfully adapted for locomotion in the air, since great extent of sur- face is secured by the expanse of feathers, without adding materially to the weight of the body. The powerful muscles that cause the quick downward movement of the wings are attached to the breastbone. This has the form of a ship's keel in flying birds and serves to cut the air, while the tail acts like a rudder to steer the bird. The hawk is able to fly at the rate of one hundred and fifty miles an hour. In bats the long, slender finger bones are covered over and connected with one another by a thin skin, and thus there is formed a very broad but light kind of wing. The 208 STUDIES IN PHYSIOLOGY flight of bats is much less rapid, however, than that of birds. Locomotion on Land. — All vertebrates living on land, with the exception of snakes and a few rare lizards and amphi- bia, are provided with two pairs of appendages. The legless snakes move forward by pushing with the posterior edge of their ventral scales, something as the earthworm uses its bristles. If compelled to move in a straight line their progress is slow; but by curving the body from side to side (as the fish moves its tail) they can glide along with considerable rapidity. Most flying birds (robins, sparrows) use their posterior appendages for perching on a support or for hopping and walking along the ground. Running birds (ostriches), on the other hand, and most domestic fowls (hens, ducks, geese) run about on their legs much like the human being. The hind legs of the four-footed mammals are used mainly for pushing the body forward, the front legs serving rather as a means of support for the head end. In dray horses, the thigh muscles have a great development, while in the animals that spring for their prey (lions, cats, tigers) the extensors in the calf of the leg are highly developed. CHAPTER XI A STUDY OF RESPIRATION 1. NECESSITY FOR RESPIRATION Definitions. — Res-pi-ra'tion (Latin re = again and again + spirare = to breathe) involves two distinct processes : first, that of taking into the body new supplies of fresh air, and secondly, that of removing from the body the impure air that has been used. To the first process is given the name in-spi-ra'tion (Latin in = into + spirare = to breathe); the second is called ex-pi-ra'tion (Latin ex = out -f spirare = to breathe). Necessity for Inspiration. — Every contraction of the mus- cles, every activity of the brain or of gland cells, involves metabolism in these various tissues. We have seen that the heart- beats more rapidly during exercise, and this means that the red blood corpuscles are being hurried into mus- cular tissue with their little boat-loads of oxygen. It is a familiar fact, too, of everyday experience, that during the activity of the various organs, we breathe more rapidly, for as oxygen is in greater demand, more must be furnished to the blood, or metabolism in the tissues will be retarded. Necessity for Expiration. — • Oxidation necessarily produces a supply of the compounds we have classed as wastes. Even when we are sleeping, the heart, the kidneys, many of the various gland cells, and some of the nerve cells are at work, and are therefore giving to the blood carbon dioxid, water, and urea. If we take violent exercise, the amount of these wastes is greatly increased, and if they are not thrown off from the body, death will ensue, for they will finally stop p 209 210 STUDIES IN PHYSIOLOGY the processes in the body just as surely as does an accumu- lation of ashes in a furnace. Wastes given off by Lungs. — If one breathes on a cold window pane, one finds that the .glass becomes clouded with vapor. This shows that by expiration the body gets rid of some of its waste water. Carbon dioxid is like- wise excreted from the lungs, as one can easily demonstrate by the milky appearance of limewater into which the breath has been blown. 2. THE ORGANS OF RESPI- RATION Course taken by the Air. — Air enters the body through the two nostrils, and then passes backward into the throat cavity. In the lower region of the throat is the slitlike glot'tis opening, through which, when the epiglottis is raised, the air FIG. 97. — Longitudinal Section of Head and Neck, showing Food and Air Passages. a = vertebral column. 6 = esophagus. c = windpipe. d = larynx. e = epiglottis. /= soft palate and uvula. g = opening of left Eustachian enters the lar'ynx, or voice box. The latter, commonly known as " Adam's apple," projects somewhat on the ventral side of the neck, and below the larynx one can feel the rings of cartilage Just above the level of the heart the tube. h — opening of left tear duct. i = hyoid bone. k = tongue. I = hard palate. m, n = base of skull. >,p,g = upper, middle, and lower turbinate bones. about the windpipe. A STUDY OF RESPIRATION 211 windpipe divides into two tubes, the right and left bron'chus, each of which supplies air to one lung (see Figs. 98 and 99). FIG. 98. — The Windpipe and its Brandies (dorsal view). Ao = aorta. M = opening from mouth. Br = bronchi. PA = pulmonary artery. D = diaphragm. P V = pulmonary vein. Gl = glottis opening. RL = right lung. H= heart. Tr = trachea (windpipe). LL = left lung. V.C.L. = inferior vena cava. Within the lungs, the bronchi branch off into a vast num- ber of very small pipes, called bron'chi-al tubes. The finest divisions of these pipes open into extremely thin-walled air so.es (Figs. 99 and 103). The Nose Cavity. — The openings into the nose cavity are guarded by a forest of projecting hairs, through which the air is strained. By this provision a considerable amount of dust is kept from entering the body. The nose itself is lined by mucous membrane which covers the vomer, the up- per surface of the hard palate, and the spongy bones which project from the lateral walls of the nose chambers. Its mu- 212 STUDIES IN PHYSIOLOGY cous secretion collects most of the dust and germs that have passed the hairs in the nostrils. Beneath this thin lining are countless branches of blood vessels, which act like small hot-water pipes to warm the air before it reaches the throat cavity. FIG. 99. —The Windpipe and the Lungs. The Throat and Larynx. — The action of the epiglottis has been already described in connection with the digestive ap- paratus (see p. 85). Except when something is being swal- lowed, the glottis is always open, thus allowing a free passage for the air from the throat, through the larynx, into the wind- pipe. All the varied sounds of articulate speech which, more than anything else, distinguishes man from other animals, are made in the larynx. The structure and action of this wonderful mechanism will be discussed in a later chapter (see chapter XIV). The Windpipe and its Branches. — The windpipe and its branches are kept open by the incomplete rings of cartilage A STUDY OF RESPIRATION 213 to which attention has already been called. They are shaped something like a letter C, the open ends toward the dorsal surface being joined by the con- nective tissue that surrounds the windpipe and joins the rings to one another. When food is not being swallowed, the windpipe presses dorsally and closes the esophagus. As food passes down- ward, however, one can feel the esophagus push the air tube ven- trally. The mucous lining of the wind- pipe and its branches is especially interesting. The cells are more or less cylindrical or club-shaped, and their inner ends, which line the air passages, are covered by minute cilia much like those that cover a paramecium (Figs. 96 and 102). The cilia alternately wave upward toward the throat with a quick movement, and then slowly recover their former position. In this way any dust particles that have passed the Carrier of hairs at the nostril openings, and the mucus secreted by the membrane, are moved steadily upward until they reach a point where they can be coughed out into the mouth cavity. The Lungs. — One can get a good idea of the structure of the human air-passages and lungs by securing from the butcher the "haslet" of a sheep or a calf. This consists of the larynx, the windpipe, the bronchi, and the two lungs, between which lies the heart inclosed in the pericardium. A piece of the diaphragm is often attached to these organs. FIG. 100.— Dorsal View of Larynx and Windpipe cut longitudinally. a, c, t = cartilages of larynx. 6, 6' = bronchi. e = epiglottis. h = hyoid bone. tr = windpipe. 214 STUDIES IN PHYSIOLOGY Connective tissue on the outside of the windpipe. Connective tissue. ^ Ciliated cells ol / lining of wind- / Pipe. FIG. 101. — Section of Wall of Windpipe, magnified about 50 times. Photo- graphed through the microscope. The lungs are composed of soft pink tissue, easily com- pressed by the hands. If air is forced through a tube inserted in the glottis opening, the lungs swell, and when fully distended they occupy a space several times their size when collapsed. Just as soon as ona ceases to blow into the lungs, one sees that they begin to collapse, and soon reach their former condition. If it were possible for us to trace out the finest branches of the bron- chial tubes, we should find that Flo. 102. -Ciliated Cells from each one ended in a branching the Lining of the Windpipe of a^r sac W^j1 extremely thin walls a Rabbit, highly magnified. « , , . , . ,TT1_ of elastic tissue. When air comes m,1 m,2 w3=mucous cells in vari- ous stages of secreting mucus, into these air chambers, they are A STUDY OF RESPIRATION 215 FIG. 103. — Two Air Sacs with their Branches. expanded; but as expiration begins, the elastic walls help to force back through the branches of the windpipe the air that has been taken into the lungs (Fig. 103). Blood Supply. — The pulmonary ar- tery, as we have learned, arising from the right ventricle, soon divides into two branches, one for the right and one for the left lung. Within the lung tissue each blood vessel divides into small arteries that follow the course of the bronchial tubes to the « = ending of a bronchial air sacs. Here the arteries communi- tube. .,. .„ . ... 6 = pouches from air sacs, cate with a maze of capillaries which run just beneath the thin lining of the air sacs. It is here that the exchange of material takes place be- tween blood and the in- haled air, for the two are separated only by the extremely thin walls of the air sacs and of the capillaries. From the pulmonary capillar- ies of each lung the blood is carried back to the left auricle by two pulmon- ary veins. FIG. 104.— Blood Capillaries (injected) in The lungs, like all Walls of Air Sacs. White Spaces are the other organs of the Cross Sections of Air Sacs. Dark Lines are the Capillaries, magnified about 30 body, have a certain times. Photographed through the mi- amOunt of work to do. Material must therefore be provided to supply the waste of the tissues. This is fur- nished by a second set. of arteries (the bronchial arteries) that 216 STUDIES IN PHYSIOLOGY branch off from the thoracic aorta and supply minute capil- laries to the walls of the air tubes, air sacs, and to the various blood vessels; for the larger blood vessels, as well as the heart, must receive nutriment from the outside, since they cannot absorb it from within. Like the liver, then, the lungs are supplied with two kinds of blood. The Pleura. — The outer surface of each lung is covered with a thin layer of serous membrane, and the walls of the chest cavity are lined with the same kind of tissue. These two layers constitute the pleu'ra. Both surfaces secrete a serous liquid resembling that found between the two layers of the pericardium. Hence the lungs can glide over the chest wall without friction. The Structure of the Chest Cavity In the upper portion of the trunk is the cone-shaped chest cavity, which is more or less inclosed by the sternum, the ribs, the collar bones, and the spinal column. This bony framework is covered by muscle and skin. The floor of the chest cavity is formed by the tough sheet of muscle and connective tissue known as the di'aphragm (Greek diaphragma = partition wall). In this way there is formed an air-tight compartment which is com- pletely filled by the heart, the blood vessels, the esophagus, and the lungs. Enlargement of the Chest Cavity. — The chest cavity is not, like most boxes, inclosed by rigid, immovable walls. Let one empty one's lungs as completely as possible, and then place one hand on each side of the body, with the finger tips touch- ing on the ventral surface in front. On taking in a long breath, one feels the chest cavity enlarging at the sides and ventrally, so much so that, if the palms of the hands are pressed to the sides of the body, the finger tips may be separated by a considerable space. At the same time the ventral wall of the abdominal cavity is seen to be pushed forward. These movements prove that the chest cavity can be enlarged in three directions, namely, from side to side, from dorsal to ventral surface, and from anterior end to A STUDY OF RESPIRATION 217 posterior. We shall now consider the provisions of struc- ture that make this possible. Movements of the Ribs. — In our study of the skeleton, we learned that a pair of ribs is joined to each of the twelve dorsal vertebrae, and that ten of these pairs are attached to the breastbone by carti- lage. Most of the ribs, espe- cially the lower ones, do not run on a level from the spinal column to the breastbone ; the ventral ends are consid- erably lower than are the ends connected with the backbone. When we inspire, the muscles that run from the anterior part of the trunk to the ribs contract, and so the ventral ends of these bones are pulled upward toward a horizontal position. By this movement the breast- The dotted lines show the position of , . ,, , the ribs and sternum at inspiration, bone is pushed ventrally and the ribs themselves press outward at the sides (see Fig. 105). In this way the capacity of the chest cavity is increased from side to side and from dorsal to ventral regions. Structure and Movements of the Diaphragm. — When the dia- phragm is relaxed, it forms a dome-shaped partition between the heart and lungs in the chest cavity and the stomach and liver in the cavity of the abdomen (see Fig. 98, D). At the apex of this dome is a tendon formed of tough connective tissue, from which sheets of voluntary muscle run outward and posteriorly on all sides. The muscle fibers are attached to the lower end of the sternum, to several of the lower ribs, and to the lumbar vertebrae. When, during inspiration, the muscles of the diaphragm FIG. 105. — Diagram to show the Movements of the Ribs and Ster- num in Inspiration. c = cartilages of ribs. 7-5, r-6, r? = 5th, 6th, and 7th ribs. s = breastbone or sternum. . v = vertebral column. 218 STUDIES IN PHYSIOLOGY are made to contract, the central tendon is pulled posteriorly upon the stomach, liver, and other abdominal organs, and these in turn force outward the wall of the abdomen. By the action just described the size of the chest cavity is increased in its third dimension, namely, from its anterior to its pos- terior end. How the Lungs are filled with Air. — In order to understand the way the lungs are inflated, we may study to good advantage the action of the ap- paratus represented in Fig. 106.1 Over the bottom of a bell jar is stretched a piece of sheet rubber, in the center of which a marble is tied. A toy balloon or the lungs of a cat are fastened to the lower end of one of the glass tubes passing through the rubber cork in the top of the bell jar. To the upper end of the second glass tube is attached a piece of rub- ber tubing which can be tightly closed by a clamp. The bell 'jar is designed to represent the walls of the chest cavity, the sheet of rubber answers for a diaphragm, while the glass tube and rubber balloon function for the windpipe and one lung. We learned in the first chapter that the air exerts a pres- sure of fifteen pounds on every square inch of surface. In the apparatus we are describing, this pressure is the same on the inside and outside of the bell jar and of the balloon, and above and below the sheet rubber. But if we exhaust as much air as possible from the bell jar through the rubber tube, and then fasten the clamp, we reduce the pressure on the inside of the bell jar, and therefore outside the bal- loon. Air is then forced by atmospheric pressure down the 1 See -; Laboratory Exercises," No. 38. FIG. 106. — Apparatus to illustrate the Inflation of the Lungs. A STUDY OF RESPIRATION 219 tube that represents the windpipe, and in this way the rub- ber balloon is distended until it nearly tills the bell jar. At the same time, the outside pressure of the air against the sheet rubber forces it up into the bell jar, and its like- ness to the form of the diaphragm becomes even more apparent. Let us now seize the marble and pull the sheet rubber downward. The cavity within the bell jar becomes larger, and hence the inside pressure is less. More air rushes down the glass windpipe and distends still further the rub- ber lung. On releasing the marble we find that the dia- phragm moves up again to its former position, and that some of the air is forced out of the lung. The applications of the experiment to the action of the lungs are evident, and we need call attention only to certain points in which the experiment fails to illustrate the process of respiration. In the first place, the glass bell jar allows no movement forward and backward, and from side to side, as do the walls of the chest. In the human body, there- fore, a much greater expansion of the lungs is possible than in this apparatus. Again, nothing corresponding to the rub- ber tube is found in animals with lungs, for chest cavities are always free from air. And, finally, the force that gives to the human diaphragm its dome-shaped form is exerted by the anterior pressure of the abdominal organs, not by the pressure of the air, as is the case in our experi- ment. Inspiration and Expiration. — During inspiration, then, we enlarge the chest cavity by pulling upward and outward the front ends of the ribs, thus pushing ventrally the breast- bone, and by pulling the diaphragm posteriorly. A greater space is thus given for the lungs, and the air rushes in from the outside, distending the elastic lungs and keeping them in close contact with the walls of the chest cavity. Inspira- tion requires a considerable amount of muscular effort, for the cartilages attached to the ribs must be bent, and the 220 STUDIES IN PHYSIOLOGY abdominal walls must be stretched, when the stomach and liver are forced downward. As soon as the muscles that cause these movements begin to relax, the ribs sink back into their former position, the breastbone is pulled back into place, and the distended wall FIG. 107. — Diagram to show Changes in the Breastbone, Diaphragm, and Abdominal Wall in Respiration. A = inspiration. D = diaphragm. B = expiration. St = breastbone or sternum. Ab = abdominal wall. Tr = windpipe. The shaded part is to indicate the stationary air. of the abdomen presses the organs upward against the dia- phragm, which, therefore, becomes arched again. In all these ways the walls of the chest cavity close in upon the lungs, and thus help their elastic tissue to force out the air in expiration. Ordinary expiration is thus accomplished without muscular effort. A STUDY OF RESPIRATION 221 3. CHANGES IN AIR AND BLOOD DUE TO Temperature of Inspired and of Expired Air. — The tem- perature of a room in which we are living and working should be kept as near to 68° F. as possible. Under these conditions the air that enters the body is about 30° cooler than the normal temperature within the body (98 J° F.). Let one breathe upon the bulb of a thermometer, however, and the mercury soon registers over 90° F. (some heat being lost to the surrounding air). This means that the air is heated to a considerable extent within the body, and to do this the body must give up a corresponding amount of heat. Composition of Inspired and of Expired Air. — The air that enters the lungs consists of about one fifth oxygen and four fifths nitrogen. The latter is of no use to the body, and practically all of it is sent forth in expired air. About one fourth of the oxygen of fresh inspired air is taken up by the blood for use in the tissues (one and four fifths pounds each day). By the simple experiments suggested on p. 210, we dem- onstrated that the air coming out of the lungs contains considerable quantities of water and carbon dioxid. In twenty-four hours the body rids itself by this means of over half a pound (more than a half pint) of water, and of something less than two pounds (422 quarts) of carbon dioxid gas. At the same time, the air that leaves the lungs carries with it minute quantities of ill-smelling, poisonous organic compounds. It is the latter that give the smell of closeness to an occupied room that is poorly ventilated, and these make expired air unwholesome and dangerous. Changes in the Blood while passing through the Lungs -- Whatever the expired air has gained in the lungs is, of course, lost by the blood; the blood also takes in the ingredients given up by inspired air. The change of color i See "Laboratory Exercises," No. 40. 222 STUDIES IN PHYSIOLOGY from purple to scarlet, undergone by the blood in the pul- monary capillaries, is due, as we proved on p. 121, to the absorption of oxygen. The various exchanges that take place between blood and air in the air sacs of the lungs may be stated in tabular form as follows : — OXYGEN NITROGEN WATER CARBON DIOXID ORGANIC COMPOUNDS Inspired air con- tains .... 20+% 80-% small am't .0004% none Expired air con- tains .... 15+% 80-% consid. " 4 to 5 % small am't Blood .... gains 5 +% gains loses con- loses loses small none sid. am't 4 to 5 % amount 4. HYGIENE OF THE RESPIRATORY ORGANS Hygienic Habits of Breathing. — We have called attention (p. 211), to the admirable provisions in the nose for filtering and warming the air. No such arrangements are provided in the mouth cavity. Hence, if one breathes through the mouth, one is likely to take in considerable quantities of dust and bacteria, and these, in the long run are likely to cause inflammation or other form of disease. Catarrh is an acute inflammation of the mucous membranes of the throat and nose, and it sometimes becomes so bad that these air pas- sages are more or less closed. If one has this trouble with breathing, one should at once consult a physician. Effect of Exercise on Respiration. — Not only does the heart beat more rapidly during exercise, but the rate of breathing also increases. Oxygen is thus supplied in larger quanti- ties, and more wastes are eliminated. .Deep breathing is a prime requisite for healthful living, since in this way the air is changed throughout the lungs. In short, quick breathing, on the other hand, it is only the air in the upper pulmonary regions which is thus affected. The "second wind " that the runner gets after a short time is due to the. expansion of all portions of the lung tissue. In order to A STUDY OF RESPIRATION 223 keep the chest walls flexible and capable of full enlarge- ment, regular exercise should be persisted in throughout life. Effect of Tight Clothing upon Respiration. — In an earlier part of this chapter we learned that air is pumped into the lungs when the ventral ends of the ribs are elevated and the diaphragm is pulled downward toward the horizontal posi- tion. By no other means are ths respiratory organs filled with air, and any interference with the action of either ribs or diaphragm tends to decrease the supply of oxygen and the excretion of carbon dioxid. Tight clothing about the chest and abdomen not only results in permanent distortion of the skeleton (see Fig. 79), but also it retards the move- ments by which the chest cavity is enlarged. Shortness of breath and inability to perform any great amount of muscular exercise are some of the ill effects that are experienced from tight lacing. Diseased conditions of the organs, too, may be brought about when they are thus compressed and forced out of position. It is especially important that loose cloth- ing be worn in the gymnasium, or during any vigorous exercise, in order that the muscles used in motion and respir- ation may be free to work unhampered. Diseases of the Respiratory Organs. — Colds, we have found, are inflammations of the air passages or of other regions of the body. If the malady is confined to the nose cavity, we call it a head cold ; if it is seated in the pharynx, a sore throat results. A cold on the chest is an inflammation of the windpipe or bronchi. If the bronchial tubes are affected, their lining membrane becomes swollen, a considerable amount of mucus is often secreted, and the air passages are more or less closed ; this is bron-chi'tis. And finally, if the inflammation affects the air sacs, pneu-mo'ni-a is caused. Diph-the'ri-a and membranous croup are germ diseases pro- duced by colonies of bacteria that grow in the throat. In the progress of these diseases certain poisons called tox'ins are formed by the growing bacteria, poisons which are ab- 224 STUDIES IN PHYSIOLOGY sorbed into the blood, often with, fatal results. The anti- toxin (Greek anti = against -{- toxikon = poison) treatment for diphtheria, however, has proved to be marvelously effective in dealing with this disease. In cases of pleu'ri-sy the covering of the lungs and the lining of the chest cavity (the pleura) become inflamed, the two surfaces rub against each other, and sharp pain is felt in breathing. After a time the pleura secretes an abnormal amount of fluid, which takes up space that should be occupied by the lungs. But more to be dreaded than all the diseases we have mentioned, because it is more common, is tu-ber-cu-lo'sis of the lungs, commonly known as consumption. It is said that one seventh of all the people who die are carried off by its ravages. Yet this is a preventable disease. It is always caused by the growth within the lungs of a rod-shaped bac- terium known as ba-cil'lus tu-ber-cu-lo'sis. A man may inherit weak lungs, but he will never have consumption unless he takes into his body some of these germs. Once within the body, and finding the favorable conditions furnished by a weak system, these microscopic organisms gradually but surely destroy the lung tissue unless the disease is arrested. Consumptives, in coughing, often eject masses of this wasted tissue which are swarming with living bacteria. If the sputum falls upon the floor or the street, it soon dries, and the bacteria become a part of the dust driven about by the wind. In this form they are likely to be inhaled by the passer-by, reach the lungs, and so transplant the seed of the disease. The sputum of a consumptive patient should, therefore, be carefully collected in paper receptacles which can be burned with their contents. From the facts here presented, one sees some of the reasons that should lead the public to insist on a rigid enforcement of the rules of the Board of Health with reference to spitting in public places.1 1 See " Dust and its Dangers," by Dr. T. Mitchell Prudden. G. P. Putnam's Sons. A STUDY OF KESPIRATION 225 Coughing, Sneezing, Choking. — In coughing an extra amount of air is first drawn into the lungs and then suddenly expelled through the mouth. We cough when the air passages are irritated by inflammation or by some foreign substance, which the forced expiration often dislodges and removes. Before sneezing there is a deep inspiration, and then the volume of air is usually driven out through the nose. Sneezing is caused by a tickling of the mucous membrane of the nose ; it can be prevented by pressing firmly upon the upper lip beneath the nose. When food gets past the epiglottis into the windpipe, choking results. In cases of this kind the head should be held forward (or downward in case of a child) and sharp blows struck between the shoulders. Suffocation. — We have learned that the body must be sup- plied continually with oxygen and that its wastes must be constantly removed. If this process is interrupted even for five minutes, fatal results are almost sure to follow. By suf-fo-ca'tion is meant some interference with the process of breathing. Suffocation may be due to inclosure in a small space with a limited supply of oxygen, to the inhaling of illuminating or other gas, or to immersion in water (drown- ing). In any case the patient should be at once brought out into fresh air. If water has entered the air passages, he should be turned face downward and raised by lifting the weight of his body on your hands clasped under his abdomen. In this position the water can flow out of his lungs more easily. If respiration is feeble, cold water should be applied to his face, and his chest should be slapped vigorously. If all these methods fail to restore vitality and if the aid of a physician cannot be immediately secured, artificial respira- tion should be attempted at once. This is accomplished by laying the patient on his back, with a rolled coat or other support beneath his shoulders. His mouth should be open and his tongue drawn out. His arms should then be grasped firmly at the elbows and pulled upward and parallel to each 226 STUDIES IN PHYSIOLOGY other until they come to lie above the head. In this way air is drawn in through the nose and mouth. When the elbows are carried downward and pressed upon the chest> the air is forced out of the body. These two movements should be alternated regularly every few seconds, and hope of resuscitation by this and other means should not be aban- doned until several hours have elapsed. Necessity of Ventilation. — Every act of respiration removes about five parts of oxygen from every one hundred parts of the air taken into the body, and adds to each one hundred parts over four parts of carbon dioxid, together with the poisonous organic compounds mentioned on page 221. One might breathe in this air a second time and still be able to extract oxygen from it. The presence of chemically pure carbon dioxid in air even in considerable quantity is not necessarily dangerous ; but to take into the body again the organic wastes that have once been given off, is most unhealthful. The first effect of foul air is a feeling of sleepiness and headache, and if larger quantities are in- spired, the body becomes poisoned. We see, then, the abso- lute necessity of having the air in a living room changed frequently. The air that has been once used must be removed and a fresh supply must be furnished; this is what is meant by ven-ti-la'tion. Methods of Ventilation. — It is important to remember that fresh air is not necessarily cold air, and that draughts of air are not required, indeed that they are undesirable. The problem of ventilation is that of furnishing a sufficient quantity of wholesome air of the proper temperature, and of removing the foul air. It is evident that this is rather difficult to accomplish in schoolrooms or in public halls. Air will not of itself circulate rapidly enough, and so it has to be forced into these rooms by large blowers or revolving fans in the basement. Hot-air pipes or fans are likewise often employed at the top of the ventilating flues to draw out the foul air. Since warm air is lighter than cool air, the A STUDY OF RESPIRATION 227 former should enter a room near the ceiling. As it cools it gradually settles toward the floor, and the openings into the ventilating shafts should be found at the lower part of the room. If the system works properly, there will be a con- tinuous supply of warm, fresh air, and at the same time the air that has once been used will be drawn off through the flues. Unfortunately, in most of our dwelling houses little pro- vision has been made by the builders for proper ventilation. Hence, if the rooms are heated by steam, we frequently breathe over and over some of the air that has been already expired. This can be obviated, however, by ventilating in the following way. A piece of board two or three inches wide should be fitted across the lower end of the window opening. When the lower sash is pulled down upon it, a space is left between the upper and lower sashes, through which fresh air may enter the room without causing a direct draught. In order to secure a proper circulation of air an opening of some kind should be provided at the opposite side of the room. Furnace heat is much more satisfactory than steam from the point of view of ventilation, for in this way a continual supply of fresh air is furnished. An open fireplace is one of the best means of removing foul air, and when a fire is burning a strong current up chimney is assured. Proper Methods of Sweeping and Dusting. — It is impossible to prevent all dirt particles and bacteria from entering the respiratory organs, especially when one lives in a city, yet the amount of irritation and the chances of acquiring disease can by proper care be greatly lessened. The number of germs of various kinds that may be found in a church, school- room, theater, or living room has been proved by a long series of experiments to be enormous, for with the ordinary methods of cleaning these rooms, very few of the germs are removed. When a room is swept, most of the light dust particles and bacteria are raised from the floor and mingled 228 STUDIES IN PHYSIOLOGY with the air. After a short time, the room is "dusted," often with a feather duster. The germs which may have settled on the horizontal surfaces are again whisked off into the air. Few, if any of them, are gathered up in the floor dirt, and so the room, so far as bacteria are concerned, is just as dirty as before. Experiments have demonstrated, too, that the number of germs in a room is not materially affected by ventilating currents, unless there is a strong draught. All this germ dirt can be removed, however, by the appli- cation of a few common-sense principles. In a room which has not been used for three to four hours, practically all of the germs and fine dust particles have settled out of the air upon the horizontal surfaces. Hence, it is clear that after a room has been swept (and in public halls this should be done at night), a considerable time should elapse before dusting is begun. For dusting a damp cloth should be used; in this way all the particles of dirt are collected and can thus be removed from the room. Were these methods of cleaning adopted, the air we breathe in the rooms which we occupy would be- come practically germ free, and there would be a surprising decrease in the number of colds and other diseases to which the flesh seems to be heir.1 Carpets and draperies collect and hold quantities of dust. They should therefore be removed to the open air when being cleaned, otherwise the dust will simply be driven from one part of the room to another. It is much more hygienic to have hard-wood floors covered with rugs. Dirty streets, too, are a constant source of dust infection. Most of the irritation from this source would be avoided, however, if the citizens insisted that the streets be kept watered, especially when they are swept. 1 See " Dust and its Dangers," by Dr. T. Mitchell Prudden. G. P. Putnam's Sons, New York. A STUDY OF RESPIRATION 229 5. A COMPARATIVE STUDY OF EESPIBATION Respiration in Single-celled Animals. — Amoeba, parame- cium, and other single-celled animals take in oxygen all over the surface of the body, obtaining their supply from the air that is held in suspension by the water. In these animals of small size the oxygen can easily penetrate to all portions of the protoplasm, and hence no circulatory system is neces- sary for its distribution. Carbon dioxid can likewise be sent off from all parts of the cell surface. Respiration in the Earthworm. — Eespiration in the earth- worm is carried on through the skin. Any one at all familiar with the habits of these animals knows that their skin must be kept moist, otherwise they die. The capillary blood ves- sels pass close to the surface in order to supply the blood with oxygen and to excrete the wastes. If the skin becomes dry, the blood loses a great deal of water by evaporation, and the hardened outer surface shuts off the supply of oxygen. Respiration in Fishes. — The water in which fishes live is composed of one part oxygen and two parts hydrogen (H20). Animals, however, are unable to obtain free oxygen by separating it from the hydrogen, and the oxygen they use is supplied by the air dissolved in the water. At the sides of the mouth cavity of a fish are slitlike openings. The water taken in by the mouth is forced through these open- ings, over the four or five pairs of comb-shaped gills, to the outside of the body. The single ventricle of the fish heart forces the blood out to the gills, where the arteries connect with a great number of capillaries running close to the gill surface. Here the blood takes up a supply of oxygen and loses many of its waste matters (see Fig. 60). Respiration in Air-breathing Animals. — Toads and frogs, when hatched from the egg, begin their life as tadpoles. In this state they are really fishes. They breathe by gills ; and the blood circulation is like that of a fish. While the legs 230 STUDIES IN PHYSIOLOGY are developing on the outside of the body, lungs are forming within, and by the time the tail has disappeared and the legs have become full-grown, the animal is provided with a good pair of lungs ready for air breathing. These lungs are very simple affairs, however. The whole interior is a hollow cavity connected with a short windpipe, through which the animal swallows air taken into the mouth cavity through the nostrils. In the thin walls which inclose the lungs, run the pulmonary blood vessels. The skin of the frog is always moist, and a considerable amount of respiration is carried on through this outer surface also, much as respira- tion is carried on by the earthworm. All reptiles, birds, and mammals breathe throughout life by lungs, and little, if any, respiration is carried on through the more or less thickened skin. Respiration is most complete in the birds, since air sacs, connected with the lungs, are found in the neck, wings, abdomen, and legs, and even run out, as we have already learned, into the cavities of the bones. Hence, if the windpipe were closed and an opening were made into one of these air sacs, respiration could still be carried on. Comparison of the Organs of Respiration Studied. — In single- celled animals the whole body may be said to function in respiration, since each bit of protoplasm takes from the sur- rounding water the oxygen it needs and gives off to the water its carbon dioxid. The respiratory region in worms is somewhat more lim- ited and specialized. The whole outer skin functions as a lung, but a circulatory system is rendered necessary by the size of the animal in order to carry oxygen to the internal organs and to remove the wastes from them. In all vertebrates specialization is carried still farther, well-developed gills or lungs being provided to carry on the function of respiration. In most of the vertebrate groups, too, there is a special pulmonary blood system to carry the blood to, through, and from the lungs. A STUDY OF KESPIRATION 231 The rapidity of respiration depends very largely upon the degree of activity of the animal. Earthworms and toads, for example, are rather sluggish in their movements, and therefore require a relatively small amount of oxygen. In the warm-blooded birds and mammals, on the other hand, metabolism goes on at a rapid pace, and new supplies of oxygen must be hurried into the body to help keep up this process. CHAPTER XII A STUDY OF THE SKIN AND THE KIDNEYS Characteristics of the Skin.1 — The whole outer surface of our bodies is encased in a flexible, elastic skin of varying thickness and texture. In regions like the palm of the hand and the sole of the foot, for instance, the skin is thick and tough ; the covering of the lips, on the other hand, is ex- tremely thin. Over the distal bones of the fingers and toes are the nails, and all parts of the body, with the exception of the palms of the hands and the soles of the feet, are covered with hair. Both the hair and the nails are modified parts of the skin. Uses of the Skin. — The most obvious use of the skin is the protection it affords for the muscles and other organs that lie beneath. In the second place, it has a countless number of sense organs which receive messages from the outside of the body. These are hurried in along nerve fibers to the spinal cord and brain ; and in this way we get impres- sions of temperature, of pressure, and of pain. Again, by means of the perspiratory action of the skin, the body throws off a great deal of water and small quantities of other waste matters. And, finally, as a result of the evapo- ration of this water from its outer surface, the body loses its surplus of heat, and so keeps an even temperature of 981° F. As we might infer from all these uses, the skin is a com- plex organ composed of several tissues. We shall now study its structure and see how it is adapted to perform the four functions we have just enumerated. 1 See " Laboratory Exercises," No. 42. 232 A STUDY OF THE SKIN AND THE KIDNEYS 233 1. ANATOMY AND PHYSIOLOGY OF THE SKIN Layers of the Skin. — The skin everywhere consists of two distinct layers : an outer, called the ep-i-der'mis (Greek epi— upon + derma = skin), and an inner, the der'mis. When one gets a blister by burning the skin, most of the epidermis is lifted up by an excessive amount of lymph that comes out of the bl'ood capillaries and lymph vessels. In a blister one can easily distinguish the white epidermis from the pink layers of the dermis lying beneath. Characteristics of the Epidermis. — Let one wash with soap and water the surface of any portion of one's body and then rub it vigorously. One will find that thin layers of the outer skin are easily removed and rolled into tiny cylinders. If a needle be inserted into the skin that covers a blister, the touch of the needle will be felt, but no pain is caused, nor does the blood flow. By means of these simple experi- ments we learn the following facts in regard to the epidermis : (1) the outermost layers are being constantly worn away, and hence we infer there must be a constant growth from beneath to supply this loss; (2) blood vessels are lacking in the outer skin ; and (3) nerve fibers are present in the epidermis ; for we are conscious when the covering of a blister is touched. When we examine closely the skin on the palm of the hand and the tips of the fingers, we see that the surface is covered by a great number of ridges that run in many cases more or less parallel to each other (see Fig. 108). The pat- tern formed by this succession of ridges and grooves varies on different fingers. On a given finger, however, it persists throughout life, and use is sometimes made of this fact in identifying criminals by finger prints. FIG. 108. —Surface of Palm, mag- nified, showing Ridges and Pores from Sweat Glands. 234 STUDIES IN PHYSIOLOGY If one examines the surface of the skin with a good hand lens, one can detect the openings of the sweat tubes dotting the tops of the ridges, and on a warm day the tiny drops of perspiration can be seen oozing from these pores (Fig. 108). Structure of the Epidermis. — In a section through the skin one can easily distinguish the dermis from the epidermis. The latter is composed of many layers of cells piled on each Horny layer. Epidermis. Columnar cells. Papillae of dermis containing blood vessels. Dermis. Nervous papilla of dermis. FIG. 109. — Vertical Section of Skin, highly magnified. other. On the outside surface, however, it is impossible to make out the separate cells, for this horny portion of the skin (Fig. 109) is composed of thin scales united by a cement substance. We shall soon see that these dead scales, which are easily rubbed from the surface, were once living cells. In the deepest part of the epidermis is a single layer of columnar cells standing on end (Fig. 109). These are the most active cells of the epidermis. They absorb nourishment from the lymph that oozes from the blood vessels running through the dermis, they grow, produce new cells by division, A STUDY OF THE SKIN AND THE KIDNEYS 235 and these daughter cells gradually approach the surface of the skin as the outer layers are worn away. During this process the cells become dryer and thinner, until finally all their protoplasm dies, and they become the outer horny scales to which we referred above. This layer is of special use in protecting the more delicate cells beneath. In the layers of the epidermis are certain irregular cells of very dark color known as pigment spots. They abound in the skin of a negro and give to this race its dark color. The skin of a brunette contains more pigment granules than that of a blonde. Freckles are due to an increase in the amount of this pigment, caused oftentimes by the action of the sun. Structure of the Dermis. — If a thick piece of -skin were to be soaked for a time in a weak acid or alkaline solution, one could easily pull off the epidermis from the dermis. It would then be seen that the surface of the latter is thrown up into numerous cone-shaped elevations called pa-pil'lce of the dermis, which fit into corresponding depressions in the under layer of the epidermis. These small papillae are of two sorts (see Fig. 109). One kind is supplied with loops of blood capillaries, which thus bring the blood near to the living cells of the epidermis. In the papillae of the second class are little sense organs called tactile corpuscles, from which nerve fibers run in to connect with the spinal cord and the brain.1 These highly sensitive papillae are especially numerous on the palm of the hand and the tips of the fingers. Here they are arranged in rows ; the epidermis fills in the spaces between the little mountain peaks of the same range, and thus are formed on the outer skin the ridges to which we have already referred (Fig. 108). The dermis is, therefore, well supplied with nerves and with blood vessels. The larger portion of this layer of the skin, however, is composed of loosely arranged fibers of con- 1 The consideration of the skin as a sense organ will be taken up more fully in connection with the nervous system. 236 STUDIES IN PHYSIOLOGY nective and elastic tissue. Beneath the dermis, too, there is a large amount of these tissues, in the meshes of which fat is deposited in considerable quantity. This fatty layer serves, as already stated (p. 50), to retain the heat of the body, and it is also used for fuel when needed for the pro- duction of energy. The wrinkles of old age are due to the fact that this fat has been drawn upon to such an extent that the skin fits loosely over the underlying tissues. Nails. — The horny layer of the epidermis becomes espe- cially developed in the nails of the fingers and toes. Except at their projecting ends these nails lie upon and are closely attached to the dermis, and their edges and bases are covered over by a roll of the epidermis (Fig. 110). The nail itself, like all epidermis, is not sup- FIG. no. -Section of Nail plied with blood vessels, its general and Parts beneath. pink color being due to the rich 1, 2, 4 = horny cuticle or epi- supply of blood in the papillae of ^ dermis. the dermis beneath. Near the base 9 12 = dermis. ' °^ the nail? however, these papillae are less numerous and the nail it- self is more opaque ; these facts explain the presence of the whiter area known as the lu'nu-la (Latin, luna = moon + ula = little). Nails increase both in thickness and in length by a growth from the living cells on the under surface of the nails and at their base. If the nail is accidentally torn off, a new one is produced, provided these deeper cells are not injured. Hair. — A second modification of the epidermis is the hair. To help understand the way hairs are placed in the epidermis, one might imagine the head of a fine pin to be pushed diagonally against a thin sheet of rubber in such a way as to form a deep pit without breaking the surface. The sheet of rubber would then represent the epidermis, A STUDY OF THE SKIN AND THE KIDNEYS 237 and the depression would answer to the hair fol'li-cle or pit, from which projects in a diagonal direction the shaft of the hair (represented by the pin). The root of the hair is there- fore a considerable distance from the surface of the skin; indeed, it is usually deep down in the fatty layer. Oblique section.throngh Papilla of hair a Pacinian corpuscle FIG. 111. — Vertical Section of Scalp, highly magnified. At the base of every hair is a cup-shaped depression into which projects a third kind of papilla of the dermis. TJiis is supplied with both blood vessels and nerves. All the growth of the hair takes place in the cells just above this papilla, that is, in the lower cells of the epidermis. The projecting shaft is wholly formed of dead horny cells. Hairs usually pass up through the dermis and epidermis in a diagonal direction. From the base of the hair follicle, on the side toward which, the hair slopes, minute bundles of 238 STUDIES IN PHYSIOLOGY involuntary muscle run out toward the outer regions of the skin (Fig. 111). When these muscles contract, hairs are made to assume an erect position, or in other words to " stand on end." In the skin of a cat the muscles attached to the base of the hairs are specially developed. Glands of the Skin. — Two kinds of glands are found in the skin, namely, the oil or se-ba'ceous (Latin, sebum = grease) and the sweat or per-spi'ra-to-ry glands. The former are found in most parts of the skin, being most numerous in the scalp and in the skin of the face. Like hairs, however, they are wanting on the palms of the hands and the soles of the feet. Sweat glands, on the other hand, are most numer- ous in the regions just named. One writer estimates that there are 2800 sweat pores on every square inch of the sur- face of the palm, and that the total number of these glands in one's skin is about 2,500,000. Sebaceous Glands. — In form these glands resemble small irregular sacs (see Fig. 111). The mouths of the sacs open most frequently into the cavity of a hair follicle. The cells in the interior of the gland are formed into a kind of oily secretion which keeps the hair from becoming dry and brittle. This liquid also spreads more or less over the surface of the skin and makes it oily and less permeable to water. At the edges of the eyelids the sebaceous glands are especially large and their secretion prevents the lids from sticking together. Perspiratory Glands. — We have already called attention to the pores that may be seen on the surface of the epider- mis of the hand. From one of these openings one can trace in a section of the skin a more or less spiral duct inward through the epidermis and the dermis, until in the fatty layer below the skin the little tube coils itself into a knot (see Fig. 111). In this inner region a fine capillary network runs about the cells of the gland. Here the blood and lymph Jose a considerable amount of water, together with a small amount of urea and salts. These ingredients make up the A STUDY OF THE SKIN AND THE KIDNEYS 239 perspiration. This passes upward through the twisted duct and oozes out through the pore upon the surface. Hence the skin, in addition to its protective and sensory functions, is also an important excretory organ. There are two kinds of perspiration, insensible and sen- sible. In the former the sweat evaporates as rapidly as it reaches the surface, and we are not conscious of perspiring. That the process is going on, even when we feel cool, can be demonstrated by placing the palm of the hand on a cool mirror. By far the larger amount passes off in insensible form. During exercise or on a hot day the perspiration stands in drops on the surface of the body ; this condition is known as sensible perspiration. Heat Regulation in the Body. — The temperature of the healthy human body, as we learned on p. 221, is 981° F. This does not vary to any appreciable extent in winter or summer, no matter how vigorously one may exercise. Yet during exertion metabolism goes on much more rapidly, and a great deal of heat is thereby caused. What then becomes of this extra heat ? In fevers the temperature sometimes runs ten degrees higher than the normal. At this time we know that the skin is dry and parched, for the body is unable to perspire. We may infer, then, that in health we keep cool by perspir- ing, and such proves to be the case. During exercise the heart beats with greater rapidity, and the heated blood is driven more rapidly through the skin as well as through other organs of the body. When it comes in contact with the two and a half millions of sweat glands of the skin, a great deal of water is given out, and this soon reaches the surface and collects in drops. In evaporating this water the body loses its surplus of heat, just as a stove loses heat when it causes a pan of water to pass off into the air in the form of vapor. By this automatic process our bodies keep at an even temperature, whatever may be the condition of the air or the degree of metabolism within us. 240 STUDIES IN PHYSIOLOGY 2. HYGIENE OF THE SKIN Importance of Bathing. — The sebaceous and perspiratory glands are constantly pouring their secretions in greater or less quantity upon the skin. As the water evaporates, the oil and the solid ingredients of the sweat are left behind. Unless these are removed, they tend to clog the openings of the ducts from the glands and so interfere with the work of the skin. A considerable amount of these substances is doubtless worn away, together with the scales of the outer skin, by friction against the clothing. But if the skin is to carry on its functions to the best advantage, frequent baths must be taken. Kinds of Baths. — The oily secretions and much of the accumulated dirt on exposed surfaces of the skin can be removed only by the use of warm water and soap ; hence these should be employed upon the face and hands two or three times a day and at least once or twice a week upon the whole body. Warm baths should be employed, how- ever, for their cleansing effect only, since they are usually followed by a feeling of lassitude. One is much more likely to catch cold, too, after exposure to warm water, as it opens the pores of the skin, causes the arteries near the surface to dilate, and thus increases the amount of perspiration. Unless the warm bath is taken just before going to bed, it should be followed by a quick application of cold water. Cold baths, on the other hand, if taken under proper con- ditions, have an exhilarating effect. The best time for such a bath is immediately on rising in the morning. Until one becomes accustomed to the cold temperature, the water may be applied with a sponge. The body should then be rubbed vigorously with a coarse towel. In our study of the circu- lation we referred to the effect of heat and cold upon the arteries. After their first quick contraction caused by the contact of the cold water with the skin, the blood vessels A STUDY OF THE SKIN AND THE KIDNEYS 241 enlarge, and one feels all over the body a warm, healthful glow. Baths should never be taken immediately after eat- ing, since the blood is thereby drawn away from the organs of digestion. Nor should one remain in cold water until one feels a chill. If the warm reaction does not take place after the bath, the latter is not beneficial, but injurious. Cold baths are undoubtedly one of the best means of pro- tecting the body against colds. Shower baths, however, are better than a cold plunge, for they stimulate both by the cool temperature of the water and by the force with which it strikes the skin. Care of the Hair. — The oil glands are most numerous in the scalp, and if the skin is in a healthy condition, the hair is supplied with just the proper amount of oil. If this secretion dries, however, and becomes mixed with the loose outer scales of the epidermis, dandruff is caused, and this should be removed by vigorous brushing and shampooing. Not only is the scalp cleaned in both of these ways (if clean brushes and combs are used), but the friction stimu- lates the circulation of the blood through the scalp, and good blood is a better hair tonic than any external applica- tion of the " tonsorial artist." If the oil supply is insuf- ficient and the hair becomes dry, vaseline may well be used. The scalp should be well dried after a bath, for moisture at the roots of the hair tends to cause decomposition. Care of the Nails. — One of the surest means of detecting slovenly personal habits is by watching the care an indi- vidual takes of his finger nails. An accumulation of dirt beneath the nails or jagged edges caused by biting the nails almost always indicate a want of good breeding. The finger nails should be carefully cleaned with soap, water, and a nail brush or with a nail cleaner, but never with a penknife or scissors, for metal scratches the surface and makes a place for the lodgment of dirt. The most convenient method of cutting the nails is in a curved direction, and this gives them the best appearance. The roll of epidermis about the lunula 242 STUDIES IN PHYSIOLOGY should frequently be moistened and pushed back ; otherwise this outer skin is likely to become torn and to form the so- called " hangnails." These are often a source of great dis- comfort and sometimes of danger, for they furnish a possible opening for infection by bacteria. Treatment of Burns. — We have already suggested the treatment for cuts .and bruises of the skin in connection with the blood system (see p. 153). Another form of accident that may injure the skin is a burn. The affected part should be covered with a paste of baking soda, which tends to lessen the pain by keeping out the air and by reducing the inflamma- tion. A mixture of linseed oil and limewater (known as carron oil) is also a good remedy to keep on hand for burns. If the clothing of a person catches fire, the flames should be extinguished by wrapping him quickly in thick clothing or pieces of carpet. Clothing. — The warmth of certain kinds of cloth depends upon the fact that they keep the heat of the body from escaping ; in other words, they are poor conductors of heat. Good conductors, on the other hand, allow the heat to pass off rapidly. This difference in fabrics is largely due to the way they are woven. Wool, for instance, is usually made into cloth that is loose in texture, and thus it can hold a considerable amount of air in its meshes. Now, dry air is a poor conductor of heat. Woolen clothing is therefore generally used for winter wear. Cotton and linen are tightly woven, and heat radiation through these materials is rapid. The color of clothing, too, is of considerable importance. This can be shown by experimenting with two pieces of ice, both exposed to summer heat. If we cover one piece of ice with a dark shade of cloth, and the other piece with a yellow or white shade of the same material, we shall find that the ice melts more rapidly under the former. This means that dark colors absorb the heat rays of the sun, while the light shades tend to reflect the heat. For this A STUDY OF THE SKIN AND THE KIDNEYS 243 reason we are accustomed to wear dark-colored clothing in winter and light colors in hot weather. Another important consideration that should be borne in mind in deciding upon the proper clothing for the different ' seasons is the capacity 0!* various fabrics for absorbing moisture. Wool and silk take up a great quantity of moisture and give it off slowly by evaporation. Hence in temperate and especially in changeable climates, underwear is prefer- ably made of these materials. Cotton and linen, on the other hand, can hold but a small amount of moisture ; they allow rapid evaporation, and thus expose the wearer to the danger of a chill. Frequent attacks of cold and of summer diarrhoea are said to be prevented to a considerable extent by wearing a flannel band about the abdomen. Effect of Alcohol on Body Temperature. — ." The action of alcohol in lowering the temperature, even in moderate doses, is most important. By dilating the cutaneous vessels, it thus permits of the radiating of much heat from the blood. When the action is pushed too far, and especially when this is combined with the action of great cold, its use is to be condemned." LANDOIS and STIRLING, " Text-book of Human Physiology." " A party of engineers were surveying in the Sierra Nevadas. They camped at a great height above the sea level where the air was very cold, and they were chilled and uncomfortable. Some of them drank a little whisky, and felt less uncomfortable ; some of them drank a lot of whisky, and went to bed feeling very jolly and comfortable indeed. But in the morning the men who had not taken any whisky got up in a good condition ; those who had taken a little whisky got up feeling very miserable; the men who had taken a lot of whisky did not get up at all: they were simply frozen to death. They had warmed the surface of their bodies at the expense of their internal organs." T. LATJDER BRUNTON, London, "Lectures on the Action of Medicine." 244 STUDIES IN PHYSIOLOGY 3. A COMPARATIVE STUDY OF THE SKIN The Skin of Invertebrates. — In single-celled animals like amoeba and paramecium, although the outer part of the protoplasm is more dense than the rest, this layer cannot properly be called a skin, for skin is an organ composed of several tissues. The skin of the earthworm is an important organ that serves for protection, respiration, excretion, and sensation. We have already referred to the skeleton formed by the coral and to the hard outer shells of insects, lobsters, and clams. In reality all these outside skeletons are modi- fications of the skin whereby these animals secure more efficient protection against their enemies. The other func- tions carried on by the human skin, namely, those of sensa- tion, excretion of waste matters, and the regulation of heat, cannot be performed through a hard shell. Hence for these processes specially developed organs in other parts of the body are necessary (see p. 252). The Skin of Amphibia. — In our comparative study of respiration we observed that the skin of tadpoles and frogs is always soft and moist. These animals probably carry on all four of the skin functions mentioned on p. 232, together with the additional function of respiration. The outer cover- ing of the toad is dry and warty, but none of the amphibia are supplied with scales, feathers, or hairs, structures that are characteristic of the other groups of vertebrates. At certain times of the year the outer layers of epidermis are shed by toads and frogs, and a new layer is then formed by the living cells. In the human being the outer skin is con- tinually worn off in minute bits, except after certain dis- eases, like the measles and scarlet fever, when considerable pieces come off at one time. The Skin of Fishes and Reptiles. — Fishes and reptiles, in most cases, have a characteristic outer covering composed of scales. Fish scales are usually hardened portions of the epi- dermis, projecting back ward, and overlapping like the shingles A STUDY OF THE SKIN AND THE KIDNEYS 245 on a house. A protective covering is thus formed which does not hinder in any way the locomotion of the animal. Among the reptiles there are several types of scales. Snakes are covered with a horny epidermis that is shed usually in a single piece. In the rattlesnake a curious record is kept of these inoultings, for when the rest of the skin is dropped off, the two or three end joints are merely slipped backward a little. Every moult, therefore, adds a new rattle to the chain, but since this casting of the skin occurs at irregular intervals, the string of rattles, even if complete, does not, as is commonly supposed, indicate the age of the snake. Crocodiles and alligators are incased in a covering of bony scales which are more or less firmly attached to each other, thus rendering locomotion on land slow and clumsy. These scales are composed of both epidermis and dermis. One of the most perfect means of protection found in the animal kingdom is the shell of the turtle. This is a box minus the ends, into which the animal can withdraw its head, legs, and tail. In order to understand this curious structure, one must examine the upper shell from within. There the vertebrae forming the spinal column become evident, but they are immovably attached to the shell above, except in the region of the neck and tail. The shell itself is composed partly of the modified spinous and lateral processes of the vertebrae, partly of bony plates formed in the dermis, and both of these layers are covered over by the horny epidermis. This last layer is the much-prized tortoise shell used in making ornaments. The Skin of Birds. — Feathers are the characteristic cover- ing of birds, and they are the most wonderful of all skin structures. In no other way has such a degree of lightness been combined with such extent of surface and with such strength. If we study the wing or tail feather of a chicken, we find it to be constructed as follows. The hollow quill by which the feather is attached to the skin of the bird is con- 246 STUDIES IN PHYSIOLOGY tinued through the feather to its tip as the shaft. The vane or flat surface on either side of the shaft is composed in the first place of barbs that branch out in a diagonal direction. From the side of each barb toward the tip of the feather (that is, distally) run off a row of little barbules that are supplied with tiny hooks. Along the other (proximal) side of the barb are plain barbules, and the hooks of the barbules just below catch on to these barbules when the feather is smoothed or " preened.'' The feathers on the wing overlap in such a way that in the downward stroke the surface of the wing is FIG. 112. — Portion of Feather, magnified. sh = shaft. 6 = barb. 61 = barbule with hooks. continuous. When the wing is lifted for a second stroke, the feathers separate and allow the air to pass between them with little resistance. Not all the feathers of birds are as complicated as the quill feathers just described. Ostrich plumes have no hooks on the barbules, and hence the latter do not cling together. Egret plumes consist of shaft and barbs only ; all barbules are wanting. And finally, about the beaks of some birds are simple hairlike structures, corresponding to the feather shaft. Whatever its structure may be, however, a feather, like a hair or a nail, is always a modification of the outer layers of the skin. The Skin of Mammals. — As scales are the distinguishing outer covering of fishes and reptiles, and as birds are char- A STUDY OF THE SKIN AND THE KIDNEYS 247 acterized by the possession of feathers, so the highest group of animals, the mammals, are distinguished by the presence of hair. This varies in amount from the scattered bristles on the body of a whale, and from the numerous thickened quills that protect the porcupine, to the dense hairy cover- ing of the bear or the sheep. In structure, however, all these forms of hair agree more or less closely with that already described for human hair. Many animals of this group are supplied with claws that enable them to seize and tear their prey. Claws differ from human finger and toe nails only in the fact that the former grow on all sides of the end joint of the animal's append- ages. The bone, therefore, forms the core of the claw, and it is inclosed by the layer of horn. Hoofs of horses, cows, and of deer are formed, like claws, by a horny layer that incloses the end bone of the various digits (see Fig. 84). This hoof is constantly growing, and if it is not worn away by use, it has to be pared off, as is the case when the horse is shod. The horns- of animals are of two kinds : namely, either hollow or solid. The horns of an ox are formed by a conical projection of the frontal bone, which is covered over by dermis, and this in turn is incased in a hard layer of horny epidermis. Hence, on removing the horny part, we find that it is hollow. Successive layers are formed one within another, and this kind of horn lasts throughout the life of the animal. Deer, on the other hand, grow new horns or antlers each year. In the early months two projections grow out from the frontal bone and branch with great rapidity. At first they are richly supplied with blood vessels and are covered with a soft layer of epidermis that looks and feels like velvet. Later in the year this disappears, the antlers harden, a line of separation is formed between them and the skull, and they finally drop off. The next year the process is repeated. Horns tvhich are hollow are therefore perma* nent; solid antlers are deciduous. 248 STUDIES IN PHYSIOLOGY 4. A STUDY OF THE SHEEP KIDNEY* General Appearance of the Kidney. — One can secure of any butcher the kidney of a sheep. It is inclosed in a mass of fat. On pulling this away, one finds a thin membrane of connective tissue which closely envelops the kidney. When this covering is opened, there appears a dark red organ, more or less elliptical in outline. It is somewhat flattened, too, and is hollowed in on one edge, — in fact, it has almost the exact shape of a bean seed. From the region of the hollow or hi'lum of the kidney passes out a tube called the u-re'ter (compare with Fig. 113). Large blood vessels also enter and leave the kidney in this region. Longitudinal Section of the Kidney. — If one divides this organ in halves by cutting through from its convex edge to the hilum, one can make out pretty clearly the internal structure. At the hilum the ureter expands into a consider- able cavity called the pel'vis of the kidney. Around this cavity the kidney is seen to be divided into two distinct re- gions. The outer or cor'ti-cal (Latin cortex = bark) has a dark brownish red color and is granular in appearance. The inner or med'ul-la-ry layer is made up of cone-shaped masses, and the apex of each of these pyramids projects into the pelvis of the kidney. The general appearance of the medullary layer is red and glistening. Fine lines run through the pyramids from base to apex. 5. ANATOMY AND PHYSIOLOGY OF THE HUMAN KIDNEY Position and Appearance. — In shape and general appear- ance human kidneys resemble closely these organs of a sheep. The two kidneys are attached to the dorsal part of the cavity of the abdomen in the region of the loins, and the ureters come off from the median border of each. In the longitudinal section the pyramids of the medullary layer are seen much more distinctly, however, than in the sheep iSee "Laboratory Exercises," No. 44. A STUDY OF THE SKIN AND THE KIDNEYS 249 M RV kidney described above, and the apex of each pyramid projects like a papilla into the pelvis or enlargement of the ureter (Fig. 113). Microscopical Structure. — The kidney is composed of an enormous number of complicated tubules that begin in the cortical region, pass through the medullary layer (giving the appear- ance of fine lines through the pyramids referred to at above), and finally open on the summits of the pyramids into the cavity of the organ. At the beginning of each tubule is a tiny spherical swell- ing richly supplied with a network of blood vessels (Fig. 114). Here it is probable that water oozes out of the blood and passes thence through the tortu- ous course of the tubule. The latter also is sur- rounded with blood capil- laries. Urea, salts, and other waste matters are without doubt taken out of the blood and lymph by the cells in this region of the tube, and the urine thus formed passes through the winding course of the ducts until it finally oozes out into the cavity (pelvis) inclosed by the medullary layer. Course taken by the Urine. — The urine is therefore secreted, to a large extent at least, in the cortex of the kidney, and thence passes through the pyramids of the medullary layer into the pelvis of the organ. From this cavity in each kid- ney the ureter conducts the liquid to a storage sac called the FIG. 113. — Section of Human Kidney. Ct = cortex. M = medulla. P = pelvis of kidney. Py = pyramids in medulla. RA = renal artery to kidney. RV= renal vein to kidney. U= ureter. 250 STUDIES IN PHYSIOLOGY u'ri-na-ry bladder, whence it is discharged from the body through a tube called the u-re'thra. Importance of the Kidneys. — The kidneys are organs of first importance in ridding the blood of its wastes. If they stop work altogether, death occurs in twenty-four to forty- eight hours. Fortunately 3 M vf at the skin can help to a certain extent by excret- ing an abnormal amount of urea and salts. Under ordinary conditions about three pints of urine should be given off by the kidneys of an adult in twenty-four hours. This amount is lessened if perspiration is exten- sive. Blood Supply of the Kidneys. — As we might expect from the impor- tance of their function, these organs have a gen- erous supply of blood. A large branch from the abdominal aorta (re'nal artery) enters the hilum of each kidney, divides into smaller branches, and these finally reach the parts of the tubule where the wastes are removed. The veins that collect the blood from the two kidneys (renal veins) empty into the inferior vena cava. The blood in these two veins (as already stated on p. 148) is probably the purest in the body; it comes to the kidneys almost immediately after giving up its carbon dioxid in the lungs ; and before leaving these excretory organs it loses its waste urea, salts, and water. FIG. 114.— Diagram of the Circulation in the Kidney. ai = small artery giving off a branch. 6 = parts of cortex supplied with spher- ical swellings (glomeruli). gl = spherical swellings (glomeruli) from which arises a twisted tubule. va = branch of artery to spherical swell- ing. ve = vein from spherical swelling. v = veins from tubules. A STUDY OF THE SKIN AND THE KIDNEYS 251 6. A COMPARISON OF EXCRETORY ORGANS Before making any study of the kidneys in various groups of animals, it will be well to compare the different kinds of excretory organs in man* We must first, however, distin- guish two terms, namely — Secretion and Excretion. — Glands and their functions have been referred to frequently in the preceding chapters. We have defined a gland (p. 75) as an organ that secretes any kind of a liquid. Now, the liquids made by glands are of two kinds. Some, like the saliva, gastric and pancreatic juices, are made from materials furnished by the blood, and are of great service in the economy of the body. Such fluids are called secretions. Perspiration and urine, on the other hand, are composed of highly injurious wastes. They are secreted by the glands of the skin and by the kidneys, it is true ; but since these liquids are of no use to the body, and are at once thrown off, they are called excretions. The Kidneys and the Skin. — Attention has been called to the fact that the work of the kidneys may at times be performed to a certain extent by the skin. In structure, likewise, the two organs are somewhat similar, if we com- pare one of the kidney tubules with one of the sweat glands. Each consists (1) of a region richly supplied with blood vessels where secretion is carried on, and (2) of a tortuous duct that carries off this secretion. On the other hand, in the skin the glands are completely separated from each other, while the tubules are closely massed together in the kidneys. The most striking difference is seen, however, when we compare the two excretions. The principal use of the urine is to carry off the poisonous urea ; the perspiration serves primarily to regulate the temperature of the body. The Lungs as Excretory Organs. — If respiration ceases, death ensues in five to ten minutes, and this is largely due to the fact that the wastes of the body are not being prop- erly removed. The lungs are therefore the most important 252 STUDIES IN PHYSIOLOGY of the excretory organs. Almost all the carbon dioxid formed in oxidation is given off from the lungs, very little being excreted by the kidneys and skin. Water is given off by all three organs ; urea from two (kidneys and skin). The Liver as an Excretory Organ. — We learned, on p. 100, that the bile contains the wastes produced by the destruc- tion of red corpuscles. The liver, then, besides its. func- tions of storing sugar and of secreting a digestive juice, must be regarded as an organ of excretion. The Kidneys of Vertebrates. — Hitherto it has been our plan to begin the comparative study of a given system of organs with the lowest forms of animal life, and to follow on up to the highest mammals. In the case of the kidneys the opposite plan seems preferable. Among all mammals the kidneys have a similar position and structure, and con- sist of cortical and medullary regions, the latter being made up of separate pyramids. Birds show the first striking modification in kidney structure, for in this group the cor- tex and medullary layer cannot be distinguished. Birds, too, have no urinary bladder, and the ureters empty directly into a cavity known as the do-a'ca (Latin cloaca = a sewer), into which opens also the rectum. The urine is thus mingled with waste food substances from the alimentary canal. Among reptiles, amphibia, and fishes, there is so much diversity of structure that any comparative study of excretion is impossible within a limited space. The Kidneys of Invertebrates. — In the lobster there are two so-called green glands situated in the head region near the base of the antennae, and these act as kidneys, since they have been proved to excrete urea. Each segment of an earthworm has a pair of twisted tubes that open upon the surface of the body (Fig. 38, A). These are of use in removing urea and other wastes. Hence an earthworm may be said to have twice as many kidneys as it has segments. In some other groups of invertebrates organs corresponding to kidneys have not been identified. CHAPTER XIII A STUDY OF THE NERVOUS SYSTEM The Body as a Collection of Organs. — In the preceding chapters we have discussed the digestive, respiratory, and circulatory systems and have seen that these organs furnish all parts of the body with food and oxygen. We have studied the process of oxidation whereby we keep warm and get power to do work. And, finally, we have consid- ered the bones and muscles as the organs that give support to the body and provide the machinery for all our motions. The fact has been continually emphasized that the body is composed of a great many organs, each with its special function or functions. Cooperation of the Organs. — But a human being or any other complex organism is more than a mere collection of working organs. In our definition of an organism (p. 39) we included the statement that all the various organs work together for the common good. This is what we mean by cooperation (Latin co- = together -+- operari = to work). Sup- pose we take a few instances from everyday experiences to illustrate this cooperation. When I take food into my mouth, my salivary glands pour out upon it an abundant supply of saliva. Now, the food never comes in contact with the glands. How is it, then, that they send out their secretion at just the right time and in the proper amount ? The same questions may be asked with reference to the gastric and pancreatic secre- tions. If any one attempts to strike me in the eye, my eyelids instantly close, and my hands fly up in front of my face to ward off the blow. 253 254 STUDIES IN PHYSIOLOGY Or let us take a more complex example of cooperation between the different organs. Suppose I am a batsman on the baseball field, and a ball, thrown by the pitcher, is coming swiftly toward me. For an instant I wait with every muscle rigid ; then my arms swing the bat to strike vigorously at the passing ball. If I am fortunate enough to make a hit, my hands at once drop the bat, and my legs begin to carry me swiftly toward first base. On reaching this goal, if I stopped to consider the physiological condi- tion of my body, I should find that my heart was pumping twenty to fifty times more per minute than it was when I started ; that my rate of breathing was more rapid ; and that the flow of perspiration had been considerably increased. I should doubtless experience a feeling of satisfaction that I had not been " struck out " by the pitcher, and a determi- nation to complete the run of the bases and thus make a score for my team. Functions of the Nervous System. — All the succession of activities just described would be utterly impossible if some means were not provided for making the organs work together for the common good. The arms could not see to strike at the ball ; the legs could not make themselves run toward first base ; nor could the heart, lungs, and skin respond to the sudden exertion of the rest of the body. It is the nervous system that controls the action of each of the organs in our body and brings about a cooperation between them. All our sensations, too, and our will power are doubt- less correlated with the activities of the nervous system. Parts of the Nervous System. — The nervous system may be said to consist of nerve centers and nerve trunks. The principal nerve centers are in the brain and spinal cord. These are sometimes said to constitute the central nervous system or cer'e-bro-spi'nal center (Latin cerebrum = brain). We have already seen that these delicate organs are inclosed and wonderfully protected by the bony cranium and spinal column. A STUDY OF THE NERVOUS SYSTEM 255 •^^w— FIG. 115. — Diagram illustrating the General Arrangement of the Nervous System. 256 STUDIES IN PHYSIOLOGY From either side of this nerve center pass off numerous bundles of nerve fibers; these are sometimes called nerve trunks or simply nerves. As they approach the different organs of the body they divide into branches, and thus the nerves become smaller and smaller. Finally, the microscope is needed to trace the individual nerve fibers to their end- ings in muscle, gland, or sense organ. By means of these countless nerve fibers all parts of the body are put in com- munication with the nerve centers (see Fig. 115). Since the structure and functions of the brain are exceed- ingly intricate and difficult to understand, we will first study the least complicated part of the cerebro-spinal nerve center, namely the spinal cord. 1. ANATOMY OF THE SPINAL CORD Shape and Size. — The spinal cord is more or less cylin- drical in shape. Its length in an adult is about a foot and a half. If one measures this distance posteriorly from the base of a man's head, one will find that the cord terminates in the small of the back (near the first lumbar vertebra). Its average diameter from side to side is about three- quarters of an inch. Since its dorsal and ventral surfaces are somewhat flattened, a piece of the cord might be com- pared in its general form and size to one's little finger. The spinal cord is not of the same size, however, through- out its whole extent. In the lower neck region its diameter increases considerably ; this is the so-called cer'vi-cal enlarge- ment. A second expansion, the lum'bar enlargement, occurs near its posterior end. These two enlargements are found where collections of nerves run off to the arms and the legs. Posterior to the lumbar enlargement the cord tapers off and ends in a slender thread (see Fig. 121). Fissures. — Along the ventral surface of the cord runs a deep groove, and a corresponding though much shallower groove furrows the dorsal surface. By these so-called dorsal A STUDY OF THE NERVOUS SYSTEM 257 Ventral nerve-root and ventral fissures the spinal cord is partly divided into right and left halves (see Fig. 117). Coverings of the Cord. — Three distinct coverings surround the cord. The outside one is a loose sheath of tough con- nective tissue ; it is called the dura mater (Latin dura = hard + mater = mother, probably because of the protec- tion it affords). The innermost of the three mem- branes, the pia mater (Latin pia = gentle + mater = mother), is a thin covering, well supplied with blood vessels, and is closely at- « tached to the cord. Between the dura and pia mater is a third layer of loose connective tissue with an appearance some- pa,urtorp,lin.ry- thing like that Anterior^ of a spider's web ; from this fact it is FlG' 116> ~~ Piece of sPinal Cord, showing its Three Coverings and the Roots of the Spinal Nerves, called the a-rach1- noid (Greek, meaning like a spider's web). Within the meshes of the arachnoid is a watery fluid (cerebro-spinal fluid) somewhat like lymph in composition. The spinal cord, then, is successively wrapped about and protected by the following coverings, — skin, muscle, bony arches of the vertebrae, dura mater, arachnoid with its liquid, and pia mater. Cross Section of the Cord. — When one looks at the cross Dorsal nerve-root Dorsal ganglion '«ntr»l nerve-raot Spinal cord 258 STUDIES IN PHYSIOLOGY section of the cord, apparently two kinds of material, known as gray and white matter, can be distinguished. In the interior of the cord is the gray matter in a form somewhat resembling that of a capital H. The two projections of the H that extend toward the ventral face of the spinal cord are called the ventral horns of the gray matter ; the two dorsal horns extend in the opposite direction to the outer surface of the cord. Running across the cord and connecting the two halves is a bridge of gray matter, the gray coin' mis-sure. The H -shaped A tfferefi '/ r/erres to vcf faffer* Oorsa/ fissure Centra/ f/ssure fiferert serves from spincr/cortf mass of gray matter is sur- rounded by the white matter which consti- tutes the re- mainder of the cord. Nerve Cells and Fibers. — TJie unit of struc- ture in the nerv- ous system, as in other tissues of the body, is the cell with its processes. Nerve cells, how- ever, are more varied in form and more complex in structure than any other cells in the body. When the ventral horns of the gray matter are sufficiently magnified, one sees irregu- lar bits of protoplasm, shaped more or less like triangles or polygons. From the angles of each cell body project numer- ous fine processes that look like tiny branching roots. These are the protoplasmic processes. Another fiberlike process, how- ever, has fewer branches than the others, and can be traced for a considerable distance from the cell body. This is called an axis cylinder process ; it is the beginning of a nerve fiber. A short distance from the cell body the axis cylinder FIG. 117. — Diagram of Cross Section of Spinal Cord. Showing the H-shaped gray matter, inclosed within the white matter. Also a diagrammatic represen- tation of the afferent, efferent, and connecting fibers used in reflex action. A STUDY OF THE NERVOUS SYSTEM 259 becomes surrounded by a thick covering, called the med'ul-la-ry sheath. Nerve fibers outside the spinal cord are covered by a very thin outer membrane, known as the prim'i-tive sheath. (A common lead pencil might be used to present to the eye the structure of such a nerve fiber. The "lead" or graphite in the center of the pen- cil corresponds in posi- tion and form to the axis cylinder of the nerve fiber ; the wood surround- ing the lead answers to the medullary sheath ; and the thin layer of paint or varnish on the outside of the pencil rep- resents the primitive sheath of the nerve.) In all parts of the gray matter we find nerve cells. While they vary greatly in form and size, almost all have a cell body with protoplasmic processes and a single axis cylinder process. These axis cylinders, usually after a more or less tortuous course, divide into very fine branches and FIG. 118. — Branched Nerve Cell from Spinal Cord. a = long axis cylinder. ' 6 = branching protoplasmic processes, c = supporting tissue. FIG. 119. — Medullated Nerve Fiber. In the center is the axis cylinder. The black lines on either side repre- sent the medullary sheath. On the outside represented in white is the thin primitive sheath in which is a nucleus. thus form a so-called terminal brush. We shall find that these cells and fibers perform the important function of connecting or coordinating the various parts- of the cord. 260 STUDIES IN PHYSIOLOGY Fia. 120. — Portion of Spinal Cord, magnified 30 times. Photographed through the microscope. Upper three fourths of photograph is gray matter containing nerve cells (irregular black spots), with their processes and axis cylinders (black dots and lines) . Lower fourth of pic- ture is white matter, showing five bundles of nerve fibers. Between these bundles are seen the cross sec- tions of axis cylinders (small black dots), each surrounded by medullary sheath (white circle) . Nerve cells and proto- plasmic processes are gray in color, and since they constitute the most impor- tant part of the gray mat- ter of the nervous system, they give the latter its characteristic shade. The white color of the outer portion of the spinal cord is due to the presence of the medullary sheaths, which in a fresh condi- tion are white and glis- tening. Among the nerve cells and fibers one finds a tis- sue similar to connective tissue and numerous blood vessels ; the former serves as a supporting frame- work, the latter bring the nutrients and oxygen that are necessary for nervous metabolism. 2. ANATOMY OF THE SPINAL NERVES Number of Nerves. — While studying the skeleton we called attention to a row of holes on either side of the spinal column. Through these openings between the verte- brae (intervertebral foramina) there pass laterally from the spinal cord the spinal nerves, of which there are thirty-one pairs. These are arranged in five groups, named accord- ing to the region of the vertebral column from which they make their exit. The following table shows the relation A STUDY OF THE NERVOUS SYSTEM 261 between the number of nerves and the number of vertebrae in each region : — NUMBER OF NAME OF EEGION PAIRS OF NERVES NUMBER OF VERTEBRA Cervical . 8 7 Dorsal 12 12 Lumbar . 5 5 Sacral Coccygeal 5 1 5 (united into one) 4 (united into one) Total 31 33 (child) 26 (adult) Distribution of Nerves. — Five of the nerves on each side that come from the cervical enlargement, after uniting more or less with each other, pass down the arm, supplying its various muscles and sense organs. To the hips and the legs, likewise, are distributed most of the nerves from the lumbar enlargement. All the spinal nerves, after their exit from the spinal column, divide into smaller and smaller branches, and these reach all parts of the trunk and the appendages (see Fig. 115). Origin of the Nerves. — Each spinal nerve arises from the cord by two so-called roots. From the dorsal surface of the spinal cord on each side, a white nerve trunk passes outward to form the dorsal root of the nerve. Strands of fibers that originate in the gray ventral horn unite to form the ventral root. These two roots come together within the bony cavity of the spinal column, forming the spinal nerve which we have followed out through a hole between the vertebrae to its destination in the tissues (see Figs. 116 and 117). Structure of a Spinal Nerve. — In the cross section of a spinal nerve one sees that the whole nerve trunk is sur- rounded by connective tissue. Within this outside sheath the nerve fibers are collected into bundles, and each bundle is inclosed by a covering of connective tissue, called per'i- 262 STUDIES IN PHYSIOLOGY •S neu'ri-um (Greek peri = around + neuron = nerve.) l And finally, each fiber consists of an axis cylinder wrapped up in the medullary and primitive sheaths. Now, the essential part of every nerve fiber is its axis cylin- der, for this carries the nerve impulse from the cell body to another cell with which it is connected. Hence a nerve trunk may be compared to a cable composed of separate bundles of telegraph wires, in which each individual wire (corresponding to the axis cylinder of a nerve) is sepa- rated or insulated by its covering from its neighbor (Fig. 122). Structure of a Spinal * | f -3 § Ganglion. — The dor- 1? "I, U '§ § sal root of every & § 8 •§ spinal nerve has an i - <» jl enlargement, called ^3 a spinal gan'gli-on $ <=$ (Greek ganglion = a •o swelling). These ganglia are very small nerve centers, and consist largely of nerve cells. Many of i In much the same way the smaller bundles of muscle are sur- rounded and held together by the connective tissue called perimysium. S£ I .^ "2 1 | A STUDY OF THE NERVOUS SYSTEM 263 these nerve cells, however, have two long processes : one comes in along the nerve trunk from the organs of the body, the other runs from the ganglion into the dorsal part of the cord, ending at length in a ter- / minal brush like those al- ready described (Fig. 117). Relation of Cells and Fibers. — The nervous sys- tem, then, is made up of a very great number of dis- FlG- 122. -Cross Section of Nerve tinct units, called nerve c . Snowing smaller bundles ot nerve fibers cells. The I'OOtlike processes surrounded by connective tissue, that reach out from the Magnified 6 times. Photographed , , , , . iii • -> through the microscope. cell bodies probably aid in bringing about cooperation between the various cells in a nerve center. And finally, the long axis cylinder which extends from each nerve cell serves like a telegraph wire to connect the distant muscle or skin with the central nerve station. The length of these slender axis cylinders some- times measures several feet, as is the case with those which run from the spinal cord to the tips of the toes 3. PHYSIOLOGY OF THE SPINAL CORD AND SPINAL NERVES Experiments on Animals. — The functions of various parts of the nervous system have been determined to a large ex- tent by experiments performed on animals. When a dog, for instance, is given ether, it is made insensible to pain, and the large nerve trunks that supply one of the front legs may then be severed near the shoulder. On recovering from the effects of the ether, the animal is found to have lost all sensation and all power of movement in this leg. But when the cut ends of the nerves are brought into contact and the 264 STUDIES IN PHYSIOLOGY nerve is allowed to grow again, the dog recovers the sense of feeling in its leg and is able to move It at will. In a second animal we may cut only the dorsal roots of the nerves to the front leg, severing these roots between the cord and the spinal ganglia. The dog is still able to move its leg, as usual. But if the paw is pinched, or even burned, the animal shows no sign that it feels any pain. When, on the other hand, only the ventral roots of these spinal nerves are cut, the dog loses all control over the mus- cles of its leg. Let the paw now be pinched, however, and the animal at once gives unmistakable signs of discomfort. Functions of Nerve Fibers. — Experiments like those just described prove beyond a doubt that the nerve impulses that result in sensation or in motion are carried by nerve fibers. It is evident, too, that the dorsal and ventral roots of spinal nerves differ in their function. We saw that sensation was destroyed by cutting the nerve fibers that enter the dorsal horns of the gray matter. Hence, we conclude that the fibers in the dorsal roots carry messages to the spinal cord, and, because they have this function, we call them af'fer-ent fibers (Latin ad = to -\-ferre = to carry). By the last ex- periment described above we proved that the ventral roots conduct messages from the cord to the muscles; these nerve fibers are therefore known as ef'fer-ent (Latin ex = from -f ferre = to carry) (see Fig. 117). Nerve Impulses. — We have liken }d nerve fibers to tele- graph wires, and nerve impulses have been described as messages that pass along the axis cylinders. But in mak- ing these comparisons we must remember that telegraphy and the action of the nervous system have, in all probabil- ity, little real resemblance. We know that nerves transmit impulses at the rate of about one hundred feet per second ; electricity travels thousands of miles per second. Hence a nerve impulse cannot very closely resemble what we call a telegraph message. On the other hand, this nerve im- pulse travels much too rapidly to be explained as a chem- A STUDY OF THE NERVOUS SYSTEM 265 ical or mechanical action. We must therefore admit our ignorance of the real nature of the nervous impulse that passes along the axis cylinders ; nor do we know the real nature of the changes that take place in the nerve cells after receiving the so-called message. Reflex Action. — To get an idea of the action of our own complicated system of nerve cells and fibers, let us consider the common experience of burning one's finger. If I acci- dentally touch a hot stove, my hand is withdrawn instantly, and afterward I feel the pain of the burn. This uncon- scious and automatic withdrawal of the hand is called a reflex action. We will now try to explain this 'action from what we have learned of the structure of the spinal cord and its nerves (see Fig. 117). By following the afferent fibers outward from the spinal cord, we find that some of them terminate in the dermis of the hand. When I touch the hot stove, these fiber termi- nations in my hand are roused by the stimulus of the heat into some kind of activity. The impulse thereby aroused is conducted up my arm along the axis cylinders of the afferent fibers, and soon reaches the cells in the ganglia of the dorsal roots; thence it passes along the second axis cylinder from each of these ganglion cells, and finally reaches the terminal brushes in the gray matter of the cord. From this region a stimulus is transmitted in two directions. In the first place the cells in the ventral horn are at once aroused, and a message is sent out along the efferent fibers of the ventral roots to the muscles of my arm. The muscles contract, and my hand is pulled away from the hot stove. All the events we have been describ- ing occur almost instantly and are carried on without any action on the part of the brain. While the nerve impulse is being rushed from the cord out to the muscles, a second message is hurrying through the white matter of my spinal cord toward my brain. These fibers finally terminate in the so-called sen'so-ry cells of the 266 STUDIES IN PHYSIOLOGY brain. Not until the message reaches these cells am I con- scious that I have been burned. Fortunately, however, my hand has already been removed from danger. JVoter ct/t of ,.-' cerebral cortex >''~,~ 'Ce// of cortex of <•" cfrefira/n ffferent newe- - - from cerebrum Cere0e//(/m Jfferentrterre to cerebrum — Afferent nerve to cere6e//un? Afferent rtery& fro/n sfl/na/ co ' r - -Afferent r?erre to spjra/coraf FIG. 123. — Diagram to illustrate Cells and Afferent, Efferent, and Connect- ing Fibers of Brain and Spinal Cord. Many other activities of the body, as we shall soon learn, are carried on in a reflex manner similar to that already described, and are executed entirely without our conscious effort. 4. THE SYMPATHETIC NERVOUS SYSTEM Anatomy. — Closely associated with the spinal nerves is the sympathetic nervous system. It consists of a number of gray ganglia, the nerve cells of which are connected by gray nerve fibers (fibers without the medullary sheath). Most of the sympathetic ganglia are strung together in two parallel chains that extend along either side of the spinal column A STUDY OF THE NERVOUS SYSTEM 267 from the base of the skull to the coccyx, the stomach is a large mass of nerves and ganglia known as the solar plexus, and still other masses of this gray nerve tissue are found near the vari- ous organs in the chest and abdomen. Branches from the spinal nerves connect the sympathetic ganglia with the gray matter of the cord and brain, and from the ganglia there pass off a great number of nerve fibers that supply the organs of digestion, respira- tion, and circulation. • Physiology. — The vital or- gans just mentioned carry on their work without any con- scious direction on our part. When the stomach receives food from the mouth, the pan- creas begins to secrete more rapidly the juice that will be needed to act upon this food in the intestines ; during diges- tion the muscles of the abdomi- nal arteries relax, thus allow- ing a greater blood supply in the walls of the alimentary canal; violent exercise quick- ens the action of the heart, — these and many other activi- ties of the body are controlled either directly by the sym- pathetic ganglia or indirectly In the region of . 124. — Diagram of Sympathetic System on One Side of Body. 1 = ganglia and nerve sup- plying heart = car- diac plexus. 2 = solar plexus (for stom- ach and other organs of ahdomen). 3 = hypogastric plexus (for organs of pelvic re- gion). 4, 5, 6, 7 = row of ganglia near spinal column. 268 STUDIES IN PHYSIOLOGY by impulses sent out from the brain and spinal cord. This part of our nervous machinery is called the sympathetic system because its cells and fibers make the various involun- tary muscles of the body work in harmony or sympathy with each other. 5. THE NERVOUS SYSTEM OF A FROG Reason for studying Frog's Brain. — We have stated that the human brain has a very complicated structure. This is less true of the central nervous system of other animals. For, in comparing the nervous systems of various kinds of vertebrates, one finds that in the lower groups the brain is considerably more simple. Such a brain has the frog, and the study of the central nervous system of the frog will help much toward a comprehension of the structure and functions of the human brain. The frog's brain, like that of the human being, is a con- tinuation of the spinal cord inclosed within a bony cranium. Three regions may be distinguished: the forebrain, the midbrain, and the hindbrain. Forebrain. — The forebrain consists principally of two elongated masses called the cer'e-bral hemispheres. Nerve fibers run in from the sensory cells of the nose to the anterior part of these cerebral hemispheres, and carry to the brain the impulses that give to the animal the sense of smell. For this reason these nerve trunks are known as ol-fac'to-ry nerves (Latin olfactus — smell), and the portion of the hemispheres with which they connect are called the olfactory lobes. Midbrain. — Two prominent enlargements cover the top and sides of the midbrain. They are called the op' tic lobes (Greek optikos} relating to sight), from the fact that the large nerves from the eyes enter them. On the ventral surface of the brain these two optic nerves cross each other, the nerve fibers from the right eye passing to the left optic A STUDY OF THE NERVOUS SYSTEM 269 lobe, while those from the left eye go to the right lobe. These fibers finally communicate with cells in the forebrain. Hindbrain. — Extending across the dor- sal surface of the hindbrain just behind the optic lobes is a ridge of brain tissue called the cer-e-bel'lum (Latin cerebellum = little brain). To the remainder of the hindbrain is given the name me- dul'la ob-lon-ga'ta (Latin medulla = marrow -f- oblongata = oblong). Seven pairs of nerves are connected with the medulla. The third (arising from mid- brain), fourth, and sixth pairs are dis- tributed to the muscles that move the _, FIG. 125. — Dorsal View eyeballs. The fifth and seventh nerves of Frog's Brain. bring to the brain messages from the sense organs in the skin and mucous membrane of the head region, and carry impulses from the brain to the muscles of the jaws and eyelids and face. The eighth pair of nerves, called au'di-to-ry (Latin audire = to hear), connect the ear with the brain. The ninth pair supply the tongue and pharynx, and hence are called glos'so-phar-yn-ge'al (Greek glossa = tongue + pharyngeal = v> VII = fifth and sev- referring to the throat). The distribu- nerve^8 °f tion of the tenth pair of nerves is the VIII = eighth pair widest of any of the brain or cranial i*™*0^ nerves, and for this reason it has been ix, x= ninth and named the va'qus (Latin, vagus = wan- tenth Pairs i • \ -r, 01 -,. ; -i , i of nerves, dering). Its fibers are distributed to the lungs and air passages, to the heart and blood vessels, and to the organs of digestion. The Spinal and Sympathetic Nerve Systems. — The posterior end of the medulla is continuous with the cylindrical spinal HH= cerebellum. Lol = olfactory lobes. Med — spinal cord. MH = midbrain (op- tic lobes). NH = medulla ob- longata. VH = forebrain (cer- ebral hemi- spheres) . J=first pair (olfactory) nerves. 270 STUDIES IN PHYSIOLOGY cord. Ten pairs of spinal nerves branch off from the cord and are distributed to all parts of the trunk. Three of these pairs (the first, second, and third) are distributed to the arms ; the legs are supplied by the last four pairs. From each of the spinal nerves, branches connect with the chains of sympathetic ganglia which lie on the dorsal wall of the body cavity. Hence, in general plan there is a close resemblance between the nervous system of a frog and that of man (compare Figs. 121 and 126). Summary. — For convenience we have described the central nervous sys- tem as though it were made up of two distinct parts, brain and spinal cord, each having its separate set of nerves. In reality there is no such division. We must rather consider the brain as a prolongation and modification within the head, of the spinal cord. In the region of the hindbrain this cylindrical rod or rather tube of nerve tissue is enlarged to form the medulla and cere- bellum •; farther forward are the two FIG. 126. — Ventral View enlargements of the midbrain, namely, ^e optic lobes; while the greatest expansion is noticed in the cerebral hemispheres and olfactory lobes of the forebrain. Each of the ten spinal nerves has a dorsal and ventral root, and is therefore composed cf both afferent and efferent fibers. The ten cranial nerves may be arranged in three groups : the first (olfactory), the second (optic), and the eighth (auditory) pairs always carry mes- sages to the brain, and are therefore afferent; the third, fourth, and sixth are efferent, since they convey impulses to the eye muscles j the four other pairs (fifth, seventh, ninth, Spinal Cord, and Sym- pathetic System. I-X= cranial nerves. 1-10 = spinal nerves. A STUDY OF THE NERVOUS SYSTEM 271 and tenth) are both afferent and efferent (or mixed nerves) and in this respect resemble the spinal nerves. Frog Physiology. — We are probably indebted to the com- mon frog more than to any other animal for our knowledge of general physiology. Countless experiments have been performed upon its skin, its muscles, its sense organs, and its central nervous system. Some of these experiments which throw light upon the functions of the various parts of the brain and spinal cord will now be described.1 Functions of the Spinal Cord. — When we separate the whole brain from the spinal cord by making a cut just behind the medulla, the " frog will still continue to live, but with a very peculiarly modified activity. It ceases to breathe or swal- low; it lies flat on its belly> and does not, like a normal frog, sit up on its fore paws, though its hind legs are kept, as usual, folded against its body, and immediately resume this position if drawn out. If thrown on its back, it lies there quietly, without turning over like a normal frog. Locomotion and voice seem entirely abolished. If we suspend it by the nose, and irritate different portions of the skin by acid, it performs a set of remarkable ( defensive' movements calculated to wipe away the irritant. Thus, if the breast be touched, both fore paws will rub it vigorously ; if we touch the outer side of the elbow, the hind foot of the same side will rise directly to the spot and wipe it." Functions of the Hindbrain and Midbrain. — "If, in a second animal, the cut be made just behind the optic lobes so that the cerebellum and medulla oblongata remain at- tached to the cord, then swallowing, breathing, crawling, and a rather enfeebled jumping and swimming are added to the movements previously observed. . . / The animal, thrown on his back, immediately turns over to his belly." If the cut be made on another frog just in front of the optic lobes, " the locomotion both on land and water become quite 1 In this account we shall quote from a most interesting book by Professor William James ('« Psychology," Vol. I. Henry Holt & Co.> 272 STUDIES IN PHYSIOLOGY normal, and in addition to the reflexes already shown by the lower centers, he croaks regularly whenever he is pinched under the arms." Effect of removing the Cerebral Hemispheres. — " A frog which has lost his cerebral hemispheres alone is by an unpracticed ob server indistinguishable from a normal animal. Not only is he capable, on proper instigation, of all the acts already mentioned, but he guides himself by sight, so that if an obstacle be set up between himself and the light, and he be forced to move forward, he either jumps over it or swerves to one side. . . . He is, in short, so similar in every re- spect to a normal frog that it would take a person very familiar with these animals to suspect anything wrong or wanting with him ; but even then such a person would soon remark the almost entire absence of spontaneous motion — that is, motion unprovoked by any present incitation of sense. The continued motions of swimming, performed by the creature in the water, seem to be the fatal result of the contact of that fluid with the skin. They cease when a stick, for example, touches his hand. ... He manifests no hunger, and will suffer a fly to crawl over his nose unsnapped at. Fear, too, seems to have deserted him." Functions of the Cerebral Hemispheres. — " But now if to the lower centers we add the cerebral hemispheres, or if, in other words, we make an intact animal the subject of our observations, all this is changed. . . . Our frog now goes through long and complex acts of locomotion spontaneously, or as if moved by what, in ourselves, we would call an idea. His reactions to outward stimuli vary their form too. Instead of making simple defensive move- ments with his* hind legs, like a headless frog if touched ; or of giving one or two leaps and then sitting still like a hemisphereless one, he makes persistent and varied efforts of escape, as if, not the mere contact of the physiologist's hand, but the notion of danger suggested by it were now his spur. Led by the feeling of hunger, too, he goes in A STUDY OF THE NERVOUS SYSTEM 273 search of insects, fish, or smaller frogs, and varies his pro- cedure with each species of victim. The physiologist can- not, by manipulating him, elicit croaking, crawling up a board, swimming, or stopping at will. His conduct has become incalculable — we can no longer foretell it exactly. Effort to escape is his dominant reaction, but he may do anything else, even swell up and become perfectly passive in our hands." Summary. — From all these experiments we conclude (1) that the cells and fibers of the spinal cord are able to direct reflex movements of a defensive kind, without any help from the brain ; (2) that the hind- and midbrains con- trol the processes of locomotion, swallowing, breathing, and croaking; and (3) that all the voluntary actions of the animal are governed by the f orebrain. It is probable, too, that all the messages which come in from the eyes, ears, nose, and skin reach the forebrain before the frog experi- ences any kind of sensation. 6. ANATOMY OF THE HUMAN BRAIN Protection for the Brain. — The human brain is an exceed- ingly delicate mechanism, and would be liable to frequent injury were it not well protected. In the first place, the thick growth of hair and the loose, tough scalp form out- side coverings for the head, which help to deaden the force of possible blows. Again, the arched form of the cranium and its several layers of bone tissue (two layers of hard bone separated by spongy bone) give to this brain case the greatest possible elasticity and strength. In the third place, the springiness of the curved spinal column and of the arched instep tends to keep the delicate structures within the skull from being jarred. And, finally, the brain itself is inclosed by the dura mater, arachnoid, and pia mater, which are continuous with the corresponding mem- branes about the cord. 274 STUDIES IN PHYSIOLOGY Parts of the Brain. — The human brain, like that of the frog, may be divided into three regions, the forebrain, the midbrain, and the hindbrain. The hindbrain reaches FIG. 127. — Side View of Brain and Upper Part of Spinal Cord. B = bodies of vertebrae. C= convolutions of the right cerebral hemisphere. Cb = cerebellum. M.Ob = medulla oblongata. N— spinal cord with s^pinal nerves. Sp = spinous process of vertebrae. downward through the large opening (fo-ra'men magnum) at the base of the skull and becomes continuous with the spinal cord. Since the two portions of the central nervous A STUDY OF THE NERVOUS SYSTEM 275 system last mentioned resemble each other more or less in their structure, we will consider the hindbrain first. Hindbrain. — Examining the brain from the side, we see that the relative position of medulla and cerebellum is the same as in the frog's brain. The human medulla looks like an enlarged portion of the spinal cord, and this was also true of the amphibian brain. The first striking contrast in the appearance of the two brains is the large size of the human cerebellum. In the hindbrain of man, too, a new structure appears in the shape of broad bands of nerve tissue that pass around the ventral surface of the medulla, connecting the two halves of the cerebellum. It is called the pons Va-ro'li-i (Latin pons = bridge + Varolii = of Varo- lius, so named from its discoverer), or more commonly simply the pons (see Figs. 128 and 130). Forebrain. — The cerebral hemispheres of the forebrain are enormously developed; indeed, they constitute about three fourths of the human brain. They fill the largest part of the cranial cavity, completely envelop the midbrain, and partially cover the hindbrain. A deep fissure sepa- rates the two hemispheres, and at the bottom of this fissure a broad band of white fibers runs across like a bridge from one half of the brain to the other. The surface of each hemisphere is raised in ridges ; these are called con-vo-lu'tions (Latin con-vol've-re = to roll up). The various convolutions and the fissures that separate them have been named from adjacent bones of the cranium or from the investigators who have studied them. The most promi- nent groove is the fissure of SyVvi-us, seen at the side of the brain, which divides the upper and lower portions of the cerebral hemispheres. The fissure of Ro-lan'do divides the frontal and parietal lobes. Beneath the an- terior end of each half of the forebrain is a small olfactory lobe (Fig. 128, I). Midbrain. — Little need be said of the midbrain of man except that it forms an isthmus connecting the fore- and 276 STUDIES IN PHYSIOLOGY hindbrains. The relatively small optic lobes can be seen by lifting up the cerebral hemispheres from the cerebellum. Comparison of Human and Frog Brains. — The striking contrasts Decween these two brains are these: First, in the human brain the cerebral hemispheres and cerebellum are enormously developed, and both are characterized by the presence of convolutions. In the second place, while the olfactory and optic lobes are proportionately large in the amphibian brain, in man they are relatively small. And finally, the two brains differ widely in the relation to each other of the three regions '(fore-, mid-, and hindbrains). In the frog's brain they lie in a straight line, one in front of the other; the axis of the human brain, on the contrary, is bent in three places, so that the forebrain extends back and covers the midbrain and hindbrain. Both in man and in the frog the central nervous system is hollow; hence the cavities found within the forebrain are continuous through the midbrain and hindbrain, with a small tube that runs within the spinal cord. Section of Forebrain. — In a cross section of the cerebral hemispheres one finds on the outside a covering of gray matter known as the cor'tex (Latin cortex = bark). Since this follows all the elevations and depressions on the surface of th.0 brain, it is clear that the convolutions largely increase the amount of gray matter. The interior mass of the brain is formed of white matter, in which are several important masses of gray tissue (ganglia). In the cord, as we have seen, the gray .matter is found in the central regions; in the medulla the gray and white matter are more or less intermingled ; while in the forebrain most of the gray matter is found on the outside. Microscopic Structure of the Brain —The gray matter of the brain, like that of the spinal cord, consists of countless nerve cells of various shapes and sizes, each with its several rootlike processes and its single axis cylinder process. Some of the fibers in the brain connect the dif- A STUDY OF THE NERVOUS SYSTEM 277 ferent parts of the same hemisphere ; some carry messages from one hemisphere to the other ; others bring the fore-, mid-, and hindbrains into connection with one another and with the spinal cord ; while a series composed of still FIG. 128. —The Base of the Brain. A — frontal lobe of right cerebral hemisphere. B = temporal lobe of right cerebral hemisphere. Cb = cerebellum. CC= connection between two hemispheres* M= medulla oblongata. I-XII— cranial nerves (see table on p. 279). others conduct messages into or out from the brain along the cranial nerves. In passing from one region of the brain to another, a nerve impulse may run through a dozen or more sets of cells and fibers. Indeed, the most intricate systems 278 STUDIES IN PHYSIOLOGY of telegraph wires of a great city are simplicity itself when compared with the fibers of the human brain. Sensory and Motor Cells and Fibers. — If we divide the cells of the gray matter according to their functions, we shall find at least two distinct classes. At the end of the afferent fibers are the cells of the first class. They receive the mes- sages that result in sensations, and are therefore called sen- sory cells. The afferent fibers, too, are commonly known as sensory nerves, because they bring in -these messages. In the second class are the cells from which originate the efferent fibers. The function of these cells is that of dis- patching the messages which control the work of the muscles and other organs. To these cells and to their fibers is therefore given the name motor. The Cranial Nerves. — Twelve pairs of cranial nerves arise from the base of the human brain. They leave the cranium through holes in the base of the skull, and are distributed to the muscles, skin, and sense organs of the head. The first ten pairs correspond more or less closely to the ten cranial nerves of the frog; true eleventh and tivelfth nerves are wanting in the amphibia. In the table on the following page will be found a statement of the origin, distribution, and function of each of these twelve pairs. 7. PHYSIOLOGY OF THE BRAIN The principal functions of the brain may for convenience be divided into (1) reflex activities, (2) conscious activities, and (3) habits or automatic activities. Reflex Activities. — The machinery of reflex action through the spinal cord has already been explained. Similar reflex processes constitute one of the most important functions of the brain. Suppose I inhale some pepper. A message goes up the first nerves to the cells in my brain. This mes- sage is then reflected or switched off to cells which send impulses down the nerves which control the muscles of my A STUDY OF THE NERVOUS SYSTEM 279 THE CRANIAL NERVES NAME OF NERVE KIND OF NERVE CARRIES MESSAGES FROM CARRIES MESSAGES TO MESSAGES KEBITLT IN First pair afferent sense organs in olfactory lobes, sensations of (olfactory) (sensory) mucous mem- thence to sen- smell brane of nose sory cells of forebrain Second pair afferent the sensory cells optic lobes of sensations of (optic) (sensory) in the eyes midbrain, sight thence to sen- sory cells of ' forebrain efferent motor cells of muscles that movements of J-hird pair ] Fourth pair j Sixth pair ) (motor) forebrain, out through the medulla move the eyes the eyes ' afferent teeth and sense medulla, thence sensations of (sensory) organs in to sensory touch, taste, tongue and cells of fore- pain (neural- Fifth pair and skin of head brain gia, tooth- ache) efferent motor cells of muscles of jaws movements of (motor) forebrain out and eyelids jaws and eye- thro' medulla lids Seventh paii efferent motor cells of muscles of face changing ex- (facial) (motor) forebrain out and scalp pressions of thro' medulla face and speech Eighth pair afferent sense organs of medulla, thence sensations of (auditory) (sensory) the inner ear to sensory hearing and cells of fore- balancing of brain body f afferent sense organs of medulla, thence sensations of Ninth pair (sensory) tongue and to sensory taste (glossoplmr-j and throat cells of fore- yngeal) efferent brain [ (motor) medulla muscles of movements of throat throat afferent (sensory) organs of diges- tion, respira- medulla, thence to sensory sensations of hunger, pain, Tenth pair and tion, and cir- culation cells of fore- brain etc. (vagus) efferent motor cells of muscles in or- automatic ac- (motor) medulla gans of diges- tion of heart, tion, respira- stomach, etc. I tion, and cir- Eleventh efferent motor cells of culation movements of pair (motor) brain out thro' muscles of muscles of medulla shoulder shoulder, etc. Twelfth pair efferent motor cells of muscles that movements of (motor) forebrain out move the tongue in thro' medulla tongue speaking and eating 280 STUDIES IN PHYSIOLOGY chest. I then sneeze, and thus get rid of the pepper. Coughing, winking, blushing, the flow of saliva at the sight of savory food — these are but a few of the reflex activities carried on by the brain. Conscious Activities. — As long as we keep awake, countless nerve impulses keep pouring into our brains. When the cells of the gray matter receive these impressions, we usu- ally become conscious that we are seeing, smelling, hearing, tasting, or feeling. These sensations are more or less last- ing, too, for we can recall distinctly the appearance of ob- jects that we saw yesterday, or even years ago, and we can hear again, as it were, the sounds we have heard in the past. In some unknown way these impressions are stored away in the protoplasm of our brain, and constitute our memory. Another power of which we are conscious is the ability to direct the movements of the body. I can rise from my seat, walk about, talk, or change the expression of my face as I will. Or, to return to the experience of burning my finger, I might by the exercise of my will power prevent the withdrawal of my hand from the hot stove, and if I had enough will power I might keep it there until it was scorched. Localization of Functions in the Brain. — The facts just stated have long been known, but only in recent years have we discovered that certain functions are located in definite parts of the brain. The nerves that come from the eyes, after crossing on the ventral surface of the brain, pass through the midbrain, and finally end in the cells of the occipital convolutions of the forebrain. Thus, odd as it may seem, we all see crosswise and in the back part of our heads ! The sense of hearing is located in the temporal convolutions below the fissure of Sylvius. Smell, taste, and touch have not as yet been satisfactorily localized. In the convolutions on both sides of the -fissure of A STUDY OF THE NERVOUS SYSTEM 281 Rolando are the nerve cells that control the movements of the arms and legs. If the right half of the brain in this region be injured, paralysis on the left side of the body is likely to follow. From facts like these we know that the nerve trunks, after leaving the motor cells, cross the brain and spinal cord, and supply the op- posite side of the body. This is true of nearly all the nerve trunks. A right-handed man is there- fore left-brained. One should, how- ever, guard against the idea that the brain can be divided into different re- FlG' 129'~side View of Brain, showing Localiza- tion of Functions, gions that work independently. An injury to a single region of the brain often destroys, for a time at least, all consciousness and all power of motion. This is often the result of a blow on the head. Habitual Activities — Can you remember the time when you learned to write? If so, you will recall that each letter was traced laboriously by a conscious effort of your brain to guide the muscles of your fingers. Writing, in our early years, belonged to the group of our conscious activities. But as time went on, less and less of our attention was needed for this mechanical process, until now our fingers seem to move of themselves. Walking, bicycle riding, swimming, playing the piano, putting on our clothes, conveying the food to our mouths — none of 282 STUDIES IN PHYSIOLOGY these activities require our attention. We have made these movements so many times that they have become automatic. In other words the conscious parts of our brains, our cerebral hemispheres, have trained the lower nerve centers (central ganglia, medulla, and cerebellum) to direct a good many of our everyday doings. Our attention is thus set free to carry on other kinds of work. " As every one knows, it takes a soldier a long time to learn his drill — for instance, to put himself into the atti- tude of ' attention7 at the instant the word of command is heard. . But, after a time, the sound of the word gives rise to the act, whether the soldier be thinking of it, or not. There is a story, which is credible enough though it may not be true, of a practical joker, who, seeing a dis- charged veteran carrying home his dinner, suddenly called out ' Attention!' whereupon the man instantly brought his hands down, and lost his mutton and potatoes in the gutter. The drill had been thorough, and its effect had become embodied in the man's nervous structure." — Huxley's " Les- sons in Elementary Physiology," Macmillan Company. Importance of Habit. — The tremendous importance of making our habits our allies instead of our enemies can- not be emphasized too strongly. " The hell to be endured hereafter," says Professor James, "of which theology tells, is no worse than the hell we make for ourselves in this world by habitually fashioning our characters in the wrong way. Could the young but realize how soon they will become mere walking bundles of habits, they would give more heed to their conduct while in the plastic state. We are spinning our own fates, good or evil, and never to be undone. Every smallest stroke of virtue or of vice leaves its never-so-little scar. The drunken Eip Van Winkle, in Jefferson's play, excuses himself for every fresh dereliction by saying, 'I won't count this time!' Well! he may not count it, and a kind Heaven may not count it; but it is being counted none A STUDY OF THE NERVOUS SYSTEM 283 the less. Down among his nerve cells and fibers the mole- cules are counting it, registering and storing it up to be used against him when the next temptation comes. Noth- ing we ever do is, in strict scientific literalness, wiped out. Of course this has its good side as well as its bad one. As we become permanent drunkards by so many separate drinks, so we become saints in the moral, and authorities in the practical and scientific spheres, by so many sepa- rate acts and hours of work. Let no youth have any anxiety about the upshot of his education, whatever the line of it may be. If he keep faithfully busy each hour of the working day, he may safely leave the final result to itself. He can with perfect certainty count on waking up some fine morning, to find himself one of the compe- tent ones of his generation, in whatever pursuit he may have singled out.'71 8. HYGIENE OF THE NERVOUS SYSTEM Changes in the Nervous System during Life. — The nervous system of a child at birth differs in many ways from that of an adult. In the first place the nerve cells in the cortex, when first formed, are more or less spherical in shape. During development, however, the axis cylinder and the various branching processes grow out through the tissues from the body of each cell something as roots work their way through the soil. In this way different nerve cells are brought into relation with each other and with different parts of the body. Again, when first formed, axis cylin- ders are naked and they only gradually become covered with a medullary sheath. The central nervous system also, like other parts of the body, increases greatly in size, es- pecially -during the early years of life. Both growth and development^ however, are slow, and hence only by degrees do we get control over the various organs of the body. 1 Professor James, " Psychology." Henry Holt & Co. 284 STUDIES IN PHYSIOLOGY Throughout life, too, continual use of the nerve cells in- volves a destructive metabolism of their protoplasm. This wasting process must, therefore, be succeeded by repair. Necessary Conditions for a Healthy Nervous System. — In studying the hygiene of the muscles we found that four conditions were necessary for healthy muscular activity (see p. 202). That the nervous system, too, may develop as it should and that it may do its work properly, the same four conditions are essential; namely, food, fresh air, various kinds of activity, and periods of rest. Food and Air. — It is estimated that in the nervous system of an adult human being there are at least three thousand millions (3,000,000,000) of nerve cells. Each of these cells must be supplied with nutritious food and pure air, or it becomes stunted in its growth and unable to do its proper work. These busy cells are constantly giving off carbon dioxid, water, and other wastes, and if these are not re- moved and fresh oxygen supplied, one feels (as we have learned on p. 226) a drowsiness and headache, and is unable to think clearly. Well-ventilated rooms, both by day and by night, are of prime importance in the hygiene of the nervous system. Varied Activity. — Fortunately for the well-being of the race, genius is rare, for genius is usually a kind of one- sided mental life. To develop a well-balanced brain one must be active along many lines. Experience tells us, too, that we cannot work successfully at the same task hour after hour without some change. Hence, varied activity is an important principle in sound education. The young child must, of necessity, turn, after a short time, from one lesson to another, and all lessons must at length give way to the relaxation of play. In planning the school curricu- lum we seek to develop the sensory areas of the child's brain by nature study and science; the motor cells are trained by manual training and physical exercise. Unfor- tunate is the boy who fails to find exhilaration in baseball, A STUDY OF THE NERVOUS SYSTEM 285 bicycle riding, or general athletics, for these sports, when properly regulated, besides developing strong lungs and vigorous muscles, are important means of educating the nerve cells and fibers. Not only in youth, but throughout life, must the student, the business man, or the laborer, at the end of a day's employment, find relaxation in other forms of activity. If he fails to do this, not only will he become weary of his work, but also he will finally come to lose the power of enjoying the pleasures he has been neglecting. In the later years of his life, the great naturalist, Charles Darwin, wrote as follows : " My mind seems to have become a kind of machine for grinding general laws out of large collections of facts. ... If I were to live my life again, I would have made a rule to read some poetry and listen to some music at least once every week; for perhaps the parts of my brain now atrophied would thus have been kept alive through use. The loss of these tastes is a loss of happiness, and may possibly be injurious to the intellect, and more probably to the moral character, by enfeebling the emo- tional part of our nature." Rest. — Experiments with animals show a striking dif- ference in the appearance of nerve cells before and after vigorous exercise. In the nerve cells of a bird that has been flying all day, the protoplasm has a distinctly granular appearance, which is not seen in a specimen killed before exercise. The tired nerve cells can be restored by rest alone. Experience, too, tells us that sleep is the best remedy for most of our ills. In childhood and youth an abundance of sleep is absolutely essential for healthy de- velopment. Late hours of evening entertainment or of study must never be alloived to keep growing boys or girls from having at least nine hours of dreamless sleep. Effect of Alcohol on the Nervous System. — " The effect of alcohol appears to be, as it were, to shave off the nervous system, layer by layer, attacking first the highest-developed 286 STUDIES IN PHYSIOLOGY faculties and leaving the lowest to the last, so that we find that a man's judgment may be lessened, though at the same time some lower faculties, such as the imagination and emotions, may appear to be more active than before. . . . Thus you find that after a man has taken alcohol his judg- ment may be diminished, but he may become more loqua- cious and more jolly than before. Then after a while his faculties become dull ; he gets stupid and drowsy. . . . Later on it affects the motor centers, probably the cere- bellum, so that the man is no longer able to walk, and reels whenever he makes the attempt. At this time, however, he may still be able to ride (on horseback), and a man who is so drunk that he cannot walk and cannot speak may ride perfectly well. . . . Later on the further anaesthetic action of the alcohol abolishes sensation, and its paralyzing action destroys the power of the spinal cord, so that the man is no longer able even to ride ; but still the respiratory center in the medulla will go on acting, and it is not until enor- mous doses of alcohol have been given that respiration becomes paralyzed. "Alcohol . . . makes all the nervous processes slower, but at the same time it has the curious effect of producing a kind of mental anaesthesia, ... so that these processes seem to the person himself to be all quicker than usual, instead of being, as they really are, much slower. Thus a- man, while doing things much more slowly than before, is under the impression that he is doing things very much more quickly. What applies to these very simple processes applies also to the higher processes of the mind; and a celebrated author once told me that if he wrote under the influence of a small quantity of alcohol, he seemed to, him- self to write very fluently and to write very well, but when he came to examine what he had written next day, after the effect of the alcohol had passed off, he found that it would not stand criticism." — T. LAUDER BRUNTON, London, " Lectures on the Action of Medicine/7 pp. 190, 191, 194. A STUDY OF THE NERVOUS SYSTEM 287 9. A COMPARATIVE STUDY OF THE NERVOUS SYSTEM Nerve Functions in Amoeba. — It is, of course, impossible to speak of anything like a nervous system in single-celled animals. We found, however, that the amoeba could move without any appendages, could take in food without any mouth, and could carry on the processes of digestion, respira- tion, and excretion without any stomach, lungs, or kidneys. So, too, this bit of protoplasm, although it is without a nervous system, has what we may at least call nervous irritability. If the slide over which an amoeba is crawling be suddenly jarred, the animal will pull in its false feet and assume a spherical form. It can distinguish particles of food from bits of sand, for it will surround the former with its body protoplasm ; dirt particles, on the other hand, are passed by. The amoeba is also affected by different colors of light. It moves about most vigorously when yellow ra}rs are thrown upon it ; in the presence of violet light it remains quiet. All these facts prove conclusively that the amoeba possesses something at least akin to nervous functions. The Nervous System of the Earthworm The " brain " of the earthworm consists of two small pear-shaped ganglia placed end to end across the dorsal surface of the esophagus (see Fig. 38). Several nerves connect this part of the nerv- ous system with the sense organs on the anterior end of the body. From each of the brain ganglia we have mentioned, a nerve trunk runs around to the ventral surface of the esoph- agus. There the two meet and run as a double chain to the posterior end of the body. In each segment this nerve chain has an enlargement or ganglion (each of which really consists of two parts). Nerves are given off in pairs along the side of this chain of ganglia, and connect this central nervous system with the sense organs on the surface of the body and with the muscles. Nervous Functions in the Earthworm. — Earthworms rarely 288 STUDIES IN PHYSIOLOGY come out of their burrows except at night, hence, although they have no eyes, they can distinguish light from dark- ness. These animals take in certain substances for food and refuse to take others, which indicates that they can taste or smell, or both. The contraction of the various muscles in the body wall, the movement of the bristles, the rhythmic pulsations of the blood vessels, and the action of the various glands, are all controlled by the nervous system. We know, too, that when an earthworm is cut in two, both pieces can move about for a time. Hence the ganglia in dif- ferent parts of the body can act more or less independently. The posterior region, however, soon dies. But the anterior part, which has the brain, can often develop new segments and in time become a complete worm. The Nervous System of Invertebrates and of Vertebrates. — In the earthworm, as we have just seen, the central nervous system is situated in the ventral region of the body. The same is true in starfishes, clams, lobsters, and insects. In- deed, in all invertebrates we find most of the ganglia (when they are present at all) to be ventral. Vertebrates, on the other hand, have a dorsal brain and spinal cord wholly or largely inclosed within a skull and spinal column, and most vertebrates, too, have two chains of sympathetic ganglia which extend along the dorsal region of the body cavity on each side of the spinal column, and which largely control the organs of digestion, circulation, and excretion. But while the general plan of the nervous system in all vertebrates is the same, striking differences occur in detail. This will be clearly shown by — A Comparison of Vertebrate Brains. — On p. 289 are repre- sented the brains of the salmon (fish), the frog (amphibian), the alligator (reptile), the pigeon (bird), and the dog and man (mammals). Thus we have a representative form of each of the five groups of vertebrates, and for convenience in comparison the brains, in spite of their great differences in actual volume, are represented as though they were of the A STUDY OF THE NERVOUS SYSTEM 289 Brain of Salmon. Brain of Frog. Brain of Alligator. Brain of Pigeon. Lai Brain of Dog. KO. Brain of Man. FIG. 130. — A Comparison of Brains (all represented as though they were of the same size). Left side view (except alligator's brain). HH= cerebellum. L.ol = olfactory lobe. Med = spinal cord. MH= midbrain (optic lobes). NH= medulla. Po = pons. VH= forebrain. I-XII = cranial nerves. 1, 2 = spinal nerves. same size. The following striking differences are seen as one follows the series from the fish to man : — (1) There is a gradual increase in the size of the cerebral hemispheres, until in man they constitute three fourths of the whole brain. The surface of the hemispheres in all the lower forms is smooth, and hence the cortex is usually small 290 STUDIES IN PHYSIOLOGY in extent. In the higher mammals, on the other hand, the convolutions increase enormously the gray matter on the surface of the brain, and this accounts in a large measure for the fact that man is the highest type of animal life. (2) While the relative size and importance of the cerebral hemispheres of the forebrain increase as one ascends the series from fish to man, one notes a more or less propor- tional decrease in the size of the olfactory lobes. In man the olfactory lobes are very small. Other mammals, like the dog, in which the sense of smell is keen, have somewhat larger olfactory lobes. (3) The increase in size and complexity of the midbrain and the hindbrain is not as striking as is that of the fore- brain. Yet when one compares the structure and functions of the optic lobes, the cerebellum, and the medulla of man with these parts of the brain of any of the lower groups of animals, one sees that these parts, too, develop enormously as one follows up the animal series. Doubtless one of the surest ways of determining whether an animal stands high or low in the scale of life is by making a careful study of the degree of complexity of its nervous system. CHAPTER XIV A STUDY OF THE SENSES 1. THE SENSE OP TOUCH The Sense Organs of Touch. — In our study of the skin we found that small hillocks or papillae of the dermis project outward into the epidermis, and that within many of these papillae are the terminations of afferent (sensory) nerve fibers. In some cases these terminals take the form of minute swell- ings on the nerve fibers; in other papillae there are more or less complicated tactile corpus- cles, each composed of sensory cells and a tangle of sensory fibers. In many regions, also, of the skin branching nerve fibers pass out and end in little knobs between the lower cells of the epidermis. From these terminations, whatever their form or position, nerve fibers extend to the central nervous system, and so, by a relay sys- tem of fibers, the external regions of the body are brought into communication with the sensory cells of the spinal cord and the brain., 291 FIG. 131. — A Tactile Corpuscle in a Papilla of the Dermis. a = knobs on the branches of a nerve in the papilla. n = nerve fiber ending in papilla. 292 STUDIES IN PHYSIOLOGY Sensations of Touch. — If I rub a piece of cloth over the tip of my finger, I can determine, even with my eyes closed, whether the cloth is smooth or rough. Its characteristics could be determined even more accurately by rubbing it on the lips or forehead. But if I were to apply the piece to the back of my neck, I should find the latter to be far less sensitive than are the lips and finger tips. The degree of sensitiveness of the various parts of the body can be determined very accurately in the following way. When I separate the points of a pair of scissors about three inches, and, with my eyes closed, apply the two points to the back of my neck, I can get a distinct impression of each. When, however, the points are brought within two inches of each other, they give the sensation of a single point. If the points are applied to the lips, they can be distinguished as two, even when within about one sixth inch, and on the tip of the tongue the points need be separated but one twenty- fourth of an inch. It is interesting in this connection to note that the degree of sensitiveness of a given part can be increased by train- ing. For instance, one experimenter found that on a certain portion of his arm, at the end of a week of training, he could distinguish the points as two when they were sepa- rated about three quarters of an inch; at the end of the fourth week of training, they could be felt as two even when only one sixth of an inch apart. In other words, he had by training his brain increased the sensitiveness of the area experimented upon more than four times. The following simple experiment shows how easy it is for one to be mistaken in regard to the judgment of one's sense impressions. If I close my eyes, cross my middle and fore- finger, and then place between the two finger tips a small marble or pea, I seem to be touching two distinct objects. This is due to the fact that under ordinary conditions it is impossible to touch an object at the same time with the thumb side of the forefinger and with the little finger side A STUDY OF THE SENSES 293 of the middle finger. Hence, with my eyes closed, I seem to forget that my fingers are crossed, and so draw the wrong conclusion that the two impressions are caused by two dis- tinct objects. 2. GENERAL SENSES Sensations of Temperature. — Besides the sensations of touch which we have just described, the skin has the power of. noting differences in the temperature of surrounding objects. If I put my right hand into cold water and my left into hot water, and then plunge both hands into a dish of lukewarm water, the latter will seem warm to my right hand and cold to my left. These temperature sensations may likewise be due to changes in the internal condition of my body. Thus, if I have been exercising vigorously on a windy day and then come into a room the temperature of which is 70°, I feel uncomfortably warm. Blood is flowing in large quan- tity through my skin, my temperature terminations send im- pulses to my brain, and I infer that the room is warm. If I act upon impulse, I open a window and sit in a draught. Whereas, if I should keep still until my circulation had returned to its normal condition, I should soon feel comfort- able without taking any risk of catching cold. Since the temperature sense is very delicate in the cheeks and fore- head, where the sense of touch is not well developed, many physiologists conclude that the nervous apparatus is a dif- ferent one for the senses of touch and temperature. Sensations of Pain. — When I put my finger on a hot stove, I cease to get an impression of temperature, but feel rather a sense of pain. The same is true if an object presses heavily upon any part of the skin. In health we are en- tirely unconscious of the presence of the organs of digestion, circulation, or respiration. But let any one of these in- ternal organs become deranged, and we become conscious of this fact by sensations of pain. Hence we infer that cer- tain nerves are specially adapted to carry to the central 294 STUDIES IN PHYSIOLOGY nervous system impulses that result in sensations of pain. We should regard painful sensations, like danger signals, as of use to us in preventing permanent injury to the body. Sensations of Hunger and Thirst. — If food is withheld from our bodies for a time, we become conscious of a sensation of hunger. We can get rid of this feeling, temporarily at least, by swallowing pebbles or any other indigestible substances. We therefore infer that hunger in its early stages is largely due to the condition of the mucous membrane of the stomach. But, since hunger likewise disappears if food is injected directly into the blood, we conclude that this is a general sensation belonging to the whole body. Thirst, too, while it can be relieved for a time by moistening the mucous membrane of the throat, soon reappears unless water is swallowed and absorbed by the blood, or unless water is injected directly into the blood vessels. Hence we conclude that sensations of hunger and thirst, and the feeling of satis- faction that follows the taking of food, are common sensations which acquaint us with the general condition of the whole body, and especially of the blood. 3. THE SENSE OF TASTE Papillae of the Tongue. — While studying the tongue, we called attention to certain elevations called papillae. These differ from those of the dermis in the fact that the mucous membrane follows the outline of the papillae on the tongue, and so the latter project from the surface. On the tongue there are three kinds of papillae. The Jil'i-form (Latin filum = a thread) are long and slender, and are found in great numbers along the sides and at the tip of the tongue. These regions we found (p. 292) to be most sensitive to tac- tile impressions, and so we believe that the filiform papillae send to the brain impulses that result in sensations of touch. A second class of papillae are the fun'gi-form (Latin fun- gus = a mushroom). In shape they resemble a mushroom A STUDY OF THE SENSES 295 or toadstool. They are less numerous than the filiform papillae, but can be easily recognized on the sides and top of one's tongue as rounded elevations of a deep red color (see Fig. 27). Near the back of the tongue are eight to twelve papillae of large size. Each is situated in a cup-shaped depres- sion, and hence is surrounded by a ditch, outside of which is a wall of mucous membrane. From this fact these large ele- vations are known as cir-cum-val'late papillce, (Latin circum- vallare = to surround with a wall). B \ * C FIG. 132. — Diagram of a Circumvallate Papilla, and of Taste Buds. A = section of a circumvallate e = epidermis. papilla. m = projecting hair. B = two taste buds. n = four inner cells of bud. c = outer or protective cells. t = taste buds. d = dermis. x = nerve fibers. The Taste Buds. — In the mucous membrane which covers the fungiform and circumvallate papillae are little groups of cells arranged in layers something like the leaves in a bud. The outer cells of each taste bud form a protective covering for the inner taste cells. The latter are spindle- shaped ; their outer ends project from the taste bud as hair- like processes, while the inner portion of each is connected with fine branches of the fifth or ninth pairs of cranial nerves. Taste buds like those on the papillae are also scattered here and there over the surface of the tongue and the palate. Sensations of Taste. — If I close my eyes and tightly hold 296 STUDIES IN PHYSIOLOGY my nose, and then put into my mouth successively a piece of potato, a piece of apple, and a piece of onion, I am unable to distinguish one from another. In other words, we learn that many of our foods are not tasted, but smelled. The same fact is demonstrated by an experience with a head cold, when the mucous membrane of the throat and nose cavities is so inflamed that the odorous particles do not affect the sense organs of smell; we then lose the power of "tasting" our food. In reality, we can taste but four different classes of sub- stances, namely, sweet, sour, bitter, and salt. All the vari- ous " flavors " of foods and drinks are therefore distinguished by smell, and not by taste. By the help of the taste buds alone we cannot even distinguish the sour of vinegar from that of hydrochloric acid. Before we can taste any sub- stance, however, it must be made into a solution, otherwise the sensory hairs of the taste buds are not affected. This is the reason why sand and other insoluble substances are tasteless. 4. THE SENSE OF SMELL The Nasal Cavities. — The two nose cavities are separated by a central partition composed partly of bone and partly of cartilage. These cavities communicate with the outside air by the two external nostrils, and at the back they open by the internal nostrils into the throat cavity. Each nasal cavity is separated from the cavity of the mouth by the hard palate, and from the brain by a portion of the ethmoid bone. In the latter are numerous perforations through which pass the branches of the first pair of olfactory nerves. Hence this roof of the nasal cavities is known as the crib'i-form plate (Latin cribrum = a sieve). Projecting from the outer wall of each nasal cavity, as we learned in studying the skeleton, are three thin bones, each rolled more or less like a scroll ; they are the superior, middle, and inferior spongy or turbinate bones. A STUDY OF THE SENSES 297 The Sense Organs of Smell. — The whole interior of the nose is lined with mucous membrane. This membrane, however, differs greatly in its structure in the upper or ol- factory region of each cavity and in the lower or respiratory region. In the latter one finds ciliated cells much like those which line the air passages from the throat to the lungs. In the mucous membrane of the upper or olfactory region there are at least two distinct types of cells, neither of which have cilia. Some are cylindri- cal, with branching processes near the base. These cells, like the outer cells of the taste buds, surround and support the rod-shaped olfactory cells which lie between them. The latter have a large nucleus near the middle, and from this region of the cell extend two slender processes; one runs outward between the cylindri- cal cells and projects on the surface of the mucous membrane as the so-called sensory hairs, the other seems to be continu- ous with branches of the olfactory nerve (see Fig. 134). Sensations of Smell. — During ordinary respiration we are not often conscious of sensations of smell. When, how- ever, we perceive an odor, we can increase its effect by sniffing. In this way larger quantities of air are drawn up into the olfactory regions of the nose, and so the olfac- tory cells are stimulated more intensely. The olfactory sense in man is so keen that three one-hundred-millionths doooooooo) °^ a grain of musk can be smelled. S/i. PL FIG. 133. — Cross Section of Nasal Chambers. An = cavities in upper jaw bone. Cr = perforations in ethmoid bone through which pass fibers of olfactory nerve. IT = lower turbinate bone. MT= middle turbinate bone. ST= upper turbinate bone. PI = hard palate. Sp = partition between nasal chambers. 298 STUDIES IN PHYSIOLOGY o~ The necessary conditions for distinct sensations of smell are these : (1) The odorous materials must be suspended in the air. Even when the nose cavities are filled with liquid cologne, we get no sensations of smell. (2) The mucous membrane of the nose must be kept moist. In cases of catarrh, when the amount of mucus is lessened, the sense of smell is either lost or im- paired. (3) The olfactory cells must not be stimulated continuously. After one has been in a close and even ill- smelling room for a time, one ceases to detect the odor. FIG. 134. — Diagram of Lining of Nose. A = cells lying close together. B = two cells separated. c = cylindrical (supporting) cell. n — nucleus or nuclear region of cell. r = rod-shaped (sensory) cell. 8 = distal region of cells. 5. THE SENSE OF SIGHT Protection for the Eye. — The delicate organs of vision, the eyes, are protected in a wonderful manner. In the first place, the eyeballs are set far back in bony sockets, in such a way that, even if one falls forward or if the head is struck with a large object, there is little danger that the eyes themselves will be hit. Again, each eyeball is covered by two movable lids that involuntarily fly together when any dangerous object approaches the head. And, finally, the curving eyelashes on the edge of each lid protect the eye- ball to a considerable extent from dust and dirt. The Tear Glands and Ducts. — The exposed surface of the eye is kept moist by the secretions of the tear glands. The latter lie along the outer side of each eyeball, and are about the size of an almond. From each gland the salty secretion oozes out on the under surface of the upper eyelid, and as A STUDY OF THE SENSES 299 the eyelid moves automatically at frequent intervals over the surface of the eye, the exposed portion of the eyeball is kept from drying. In the lower, inner corner of each eye one can detect a small elevation or papilla, in the center of which is an open- ing. This is the beginning of a tear duct which drains off into the nose cavity the excess of tears. An upper branch of this duct is shown in Fig. 135. If these tubes become stopped, the tears drop down upon the cheeks. This is also true when an increased quantity of liquid is FlG. 135. _ Front View of secreted in weeping. Left Eye, with Eyelid Sebaceous Glands. — Along the partly removed. edge of both lids are numerous oil ^D = tear duct. LG = tear gland, glands. Under ordinary conditions their fatty secretions prevent the tears from flowing out of the eyes. At times these sebaceous glands send out an abnormal amount of secretion. If this dries, it forms a yel- lowish rim on the edge of each lid, which may temporarily glue the closed eyelids together. Movements of the Eyes. — When I hold my head still and look at the middle region of the opposite wall of the room, I find I can, by moving my eyes, look at the ceiling, at the floor, out of a window on either of the side walls ; I can, also, look to each of the four corners of the walls in front of me. All these movements of the eyeballs are accomplished by the separate or combined action of the six muscles which extend from each eyeball to the walls of the eye socket. Experience tells me that it is impossible for me to look in one direction with my right eye and in the opposite direc- tion with my left. The two eyes, therefore, work together as one, and all the motions we have been describing are con- trolled by impulses sent out from the brain along the third, fourth, and sixth pairs of nerves (see p. 279). 300 STUDIES IN PHYSIOLOGY General Form of the Eye. — If the six muscles be severed near their attachment to the eyeball, the eye is still held in place by the large optic nerve, which enters the eyeball from behind. When removed from its socket, each eye appears to be spherical in its general shape ; but a closer examina- tion shows that the exposed region bulges outward some- what from the rest of the eyeball. FIG. 136. A = muscles of right eyeball viewed from above. B = muscles of left eyeball viewed from outer side. Ch = crossing of optic nerves. 11= second or optic nerves. ///= third nerve to eye-muscles. ER, Inf. Ob, Inf.R, S.Ob, SR = muscles that move the eyeballs. Coats of the Eye. — In a section of the wall of the eyeball one can make out three coats. The outer is composed of tough connective tissue. The portion of this coat which incloses the back part of the eyeball is called the sde-rot'ic (Greek skleros = hard). The white of the eye, which one can see beneath the eyelids, is the front region of this scle- rotic coat. The bulging part of the eye, to which we have already referred, is covered by a portion of the outer coat, called the cor'ne-a (Latin corneus = horny). Through this hard but transparent layer one can see the colored i'ris and the black pu'pil. A STUDY OF THE SENSES 301 The portion of the second coat, which lies within the sclerotic, is known as the cho'roid. It is richly supplied with blood vessels, which run through meshes of connective tissue, and its inner layers have a deep black color, which is due to dark granules of pigment much like those described in the skin (p. 235). In the region where the transparent Scl FIG. 137. — Diagram of the Eye. c = cornea. ON = optic nerve. Ch = choroid coat. PE = pigment beneath retina. CP — ciliary process. R = retina. fc = yellow spot. Scl = sclerotic. I = iris. spl = suspensory ligament. L = lens. VH = vitreous humor. cornea begins, this middle layer of the eye separates from the outer coat, turns inward, and forms the colored portion of the eye which is known as the iris (Greek iris = rain- bow). In the center of the iris is a circular perforation, the pupil, through which the rays of light pass into the interior of the eyeball. If one comes suddenly from a dark into a light room, one sees that the size of the pupil is large, but 302 STUDIES IN PHYSIOLOGY that soon this opening decreases in size, a result which is brought about by the contraction of the circular in- voluntary muscles found in the iris. The most important of the three coats of the eye is the inner, which is known as the ret'i-na; for it is this layer which is acted upon by the rays of light that enter the eye. The retina is only about one eightieth (-g^) of an inch in thickness, and yet in microscopical sections one can make out ten distinct layers. We shall not, therefore, attempt to give a minute description of this complex coat of the eye. We need only say that the optic nerve passes into each eye- ball through the sclerotic and choroid coats (Fig. 137), that its five hundred thousand or more nerve fibers run over the inner surface of the retina, and that each nerve fiber finally comes into communication with certain sensory cells lying just inside of the choroid coat ; the cells are known as the rods and cones. The Lens of the Eye. — Behind the iris is the crys'tal-Une lens, a beautiful transparent object, both surfaces of which are convex. It is highly elastic, and is attached to the cil'i-a-ry muscles of the choroid coat by a suspensory liga- ment. In a later section we shall see the wonderful ad- justments of this crystalline lens in our every act of seeing. The Humors of the Eye. — Between the back surface of the cornea and the front surface of the iris and the crystalline lens is a small cavity, which is filled with a watery liquid, the a'que-ous hu'mor (Latin aquosus = watery -f- humor = fluid). Behind the crystalline lens is another cavity of con- siderable size. This is distended by the vit're-ous hu'mor (Latin vitreus = glassy), which is perfectly transparent and resembles jelly in its consistency. The Eye as a Camera. — Any one who is at all familiar with a camera knows that by means of a lens, or a combi- nation of lenses, the scene to be photographed is made to appear upside down on the ground glass plate at the back of the camera. If the image is not clear, it is brought into A STUDY OF THE SENSES 303 focus by moving the lens nearer to or farther from the plate. In the eye, too, we have an arrangement similar to that of a camera, since the convex surfaces of the cornea and crystalline lens bring the rays of light to a focus on the sensitive rods and cones of the retina. Since, however, it is impossible for the lenses within the eye to be moved backward arid forward, focusing or ac-com-mo-da'tion of the eye must be accomplished in a different way j namely, by altering the shape of the lens. A B cm. c.p FIG. 138. — Changes in Lens in Accommodation. A = adjustment of lens for distant cm = ciliary muscle. objects. ch = choroid coat. B = adjustment of lens for near cp = ciliary process. objects. si = suspensory ligament, c = cornea. Accommodation of the Eye. — If I look out through the lace curtains of a window at a distant object, say a tree, I can see the latter more or less plainly, but the meshes of the lace appear blurred. When, on the other hand, I turn my attention to the individual threads of the curtain, the tree is no longer distinctly visible, and I become conscious, too, of a feeling of muscular effort. What takes place within the eye is probably this. The suspensory ligament is con- stantly pressing on the surface of the crystalline lens, and so tends to keep its outer surface more or less flattened. This condition enables the lens to focus clearly on the rods and cones of the retina images of distant objects; the 304 STUDIES IN PHYSIOLOGY images of objects near at hand, however, are not in good focus, and so they appear blurred. Hence, to get a clear picture of something close in front of me, I must push out- ward and so make more convex the outer surface of my crystalline lens ; this is accomplished by the contraction of the ciliary muscles of the choroid coat, to which we have already referred (p. 302 and Figs. 137 and 138). Sensations of Sight. — We will now try to see how it is that the eye helps us to get sensations of sight. If an ob- ject, say an arrow, is held in front of the eye, rays of light pass in a great many directions from every part of the FIG. 139. — The Formation of an Image on the Retina. arrow tip. A considerable number of these rays strike the convex surface of the cornea and the crystalline lens, and are thereby focused, or made to converge upon a point on the retina. In the same way the light rays from every other point of the arrow are brought to focus on the inner surface of the retina. By this means a smaller, inverted image of the arrow is projected on the inner lining of the eye. The influence of these light rays then passes through the transparent layers of the retina, and so the rods and cones become stimulated. From the region of each of these sensitive cells there ex- tend back into the brain fibers of the optic nerve. Most of them cross on the ventral surface of the brain, and pass to the midbrain; thence fibers run backward and end in the cells of the occipital lobes of the forebrain. We do not know A STUDY OF THE SENSES 305 what kind of a stimulus this is that affects the brain. While we may say that an inverted image of the objects x • we look at is formed 011 the retina, we cannot liken this to an impression on a photographic plate. For before we get any sensations of sight, the impulse must reach the cells of the forebrain, and we are sure that nothing like a photograph is taken by these brain cells. We must remember, too, that while our right eye, for instance, re- ceives an inverted image and sends impulses to the left half of the brain, we recognize the objects which we perceive as right side up and in their proper relations in space. The Blind Spot and the Yellow Spot. — The optic nerve does not enter the eyeball at a point exactly behind the center of the crystalline lens and cornea, but in a region somewhat nearer the inidlme. Since the optic fibers pass through all three coats and then spread over the inner lining of the retina, the region where the nerve enters the eye is without any rods and cones. The following simple experi- ment proves this spot to be blind. If one closes the left eye, holds this page about a foot away, and looks steadily at the cross near the top of the page with the right eye, one can also see more or less distinctly the large black dot. Let the book be slowly brought nearer, however, and the cross only is seen, for the dot has disap- peared from view. If the page is brought still nearer to the eye, both cross and dot are seen again. FIG. 140. 306 STUDIES IN PHYSIOLOGY A study of Fig. 140 will make clear the explanation of these facts we have been observing. In all three positions of the book (A, B, C) the rays of light pass from the cross in a straight line through the cornea, aqueous humor, lens, and vitreous humor, and reach a point on the retina directly behind. This is the region of keenest vision, for here the retina is thinnest and the cones are most numerous. Since the color of this portion of the retina is yellow, this is called the yellow spot. In position A the rays of light from the black dot enter the eye obliquely, and strike the retina outside the yellow spot ; hence the image is not as clear as is that of the cross. In position B the image of the dot falls upon the interior end of the optic nerve ; here rods and cones are wanting, no stimulus is sent to the brain, and we therefore call this the blind spot. When the page is brought to position (7, the light rays from the dot again fall upon the retina, and the dot reappears to our vision. Defective Eyes. — A normal, healthy eye has the power of adjusting itself so that objects become visible which are w ithin five to ten inches, or those which are as far away as a dis- tant horizon. Many people, however, find that they can see objects near at hand much more clearly than those at a distance ; in other words, they are near- sighted. Others, on the other hand, are far-sighted. These defects in vision are due to im- perfect formation of the eyeball, •IG. ltt._Tert^» Astigma- and can be corrected Qnly by the use of eyeglasses or spectacles, which should be purchased only after a careful examination of the eyes has been made by a specialist. Another very common defect of the eye is known as a-stig'« A STUDY OF THE SENSES 307 ma-tism. Many people, on looking with each eye separately at Fig. 141, find that some of the radiating lines stand out sharply defined, while others are indistinct or blurred. In reality, all the lines are equally distant from each other, and the indistinctness referred to above is due to the fact that the amount of curvature is not the same in all regions of the cornea and crystalline lens. For this reason some of the rays of light are not brought to a focus. Astigmatism, like near and far sightedness, should be corrected by the use of proper glasses, otherwise the constant eye strain is likely to cause chronic headaches and other disorders of the body. Some people, too, are unable to distinguish clearly various colors ; thus, red and green may appear the same to them. In other words, such people are color blind. This cannot be corrected by glasses, but can be to some extent by training. Hygiene of the Eyes. — The eyes have, as we have seen, wonderful powers of adapting themselves to varying con- ditions. This adaptability often leads us to abuse them. Thus, we frequently read when the light is insufficient, we look steadily at objects until we suddenly find that we can- not see clearly, and we read or study while riding in swiftly moving trains. In these and other ways we compel our eyes to make adjustments under trying conditions, and more or less eye strain is sure to follow. When we read, we should make sure that the light is sufficient, that it is steady, and that it comes over the left shoulder. The type on the printed page should be little, if any, smaller than that used in this book (ten-point type), the lines should not be close together, and the paper should not have a glossy surface to reflect the light into the eyes. One should remember, too, that the eyes, like other organs of the body, need frequent periods of rest. Hence study hours should be followed by periods in which the eyes are allowed to relax. Pupils who have defective eyesight should make this known to the teacher, and should be assigned the most favorable positions in the schoolroom. 308 STUDIES IN PHYSIOLOGY 6. THE SENSE OF HEARING The External Ear. — Attached to each side of the head is an oval, more or less flattened expansion, composed largely of cartilage and connective tissue. The irregular surface of the outer portion of the ear doubtless helps somewhat, like an ear trumpet, to converge the sound waves into the funnel - FIG. 142. — Parts of the Eight Ear. Note. — The coils of the cochlea (S) should project toward the observer. A = auditory nerve and its branches. M = outer portion of ear. B = semicircular canal. G = tube of external ear. I = utriculus. I' = sacculus. P = middle ear with chain of bones. R — Eustachian tube. S = cochlea. T = ear-drum or tympanum. like canal. This is about an inch long, and leads to the in- terior of the head. In the lining of this canal are certain wax glands ; these secrete a thin fluid which, on thicken- ing, hardens into a yellow paste, the earwax. Across the inner end of this tube of the external ear is stretched a thin membranous partition, known as the eardrum, or tym'- pa-num (Latin tympanum == drum). A STUDY OF THE SENSES 309 The Middle Ear. — Beyond the tympanum is a small cav- ity, known as the middle ear. From this cavity a narrow tube (the Eustaehian tube) about an inch and a half long communicates with the upper part of the throat cavity. If one were to go up on a high mountain, one would find that the pressure of the air on the outside of the body, and there- fore on the exterior of the eardrum, would become less, and that if some of the air in the middle ear were not to escape, the eardrums would be forced outward, and hence would be ruptured. If, on the other hand, one should go into a deep mine, the increased pressure on the outside of the drums would force them inward. All these accidents are prevented by the presence of the Eustaehian tubes, through which air can pass into and out from the middle ear, and so the pres- sure on both sides of the tympanum can be equalized. In severe head colds, as we have already seen (p. 86), the open- ing from the throat cavity into the Eustaehian tubes becomes temporarily closed. We then are conscious of a ringing sensation in the ears. The Bones of the Middle Ear. — Within the cavity of the middle ear are three tiny bones. The first, from its fancied re- semblance to a hammer, is called the mal'le-us (Latin mal- leus — a hammer) ; the second looks somewhat like an anvil, and hence is known as the in'cus (Latin incus = an anvil) ; the third has the exact form of a stirrup, and it has, therefore, received the name sta'pes (Latin FIG. 143. — Bones of Middle Ear. stapes = a stirrup). These three little bones are arranged in a chain across the cavity of the middle ear, for the handle of the malleus is connected with the tympanic membrane, the flat part of the stirrup presses c = hammer (malleus) . d — anvil (incus). /= stirrup (stapes). 310 STUDIES IN PHYSIOLOGY •HS.C against the inner ear, and the incus forms the connection between these two bones we have just mentioned. General Structure of the Inner Ear. — By far the most complex portion of our auditory apparatus is the inner ear. Indeed, so complicated is it that we shall not attempt to describe minutely its various parts. In general, we may say that the in- ner ear consists of a succession of small cavities hollowed out of the interior of the hardest part of the temporal bone; that with- in these cavities lie, more or less loosely, a series of thin-walled tubes and small sacs which are distended with a watery fluid known as en1- do-lymph (Latin endo = within + lymplia = wa- ter) ; that the spaces between these membranous cavities of the ear and the outer bony walls are filled with liquid per'i- tymph (Greek peri = around -f Latin lymplia = water) ; and that finally, and most important of all, the fibers of the eighth or auditory nerve run to certain portions of the membranous sacs and tubes which are especially sensitive to sound waves. The Structure and Functions of the Semicircular Canals. — The flattened portion of the stirrup bone is fastened to a thin- FIG. 144. — Distribution of Auditory Nerve (dia- grammatic) . A.N = auditory nerve. ASC, HSC, PSC = a swelling on each of the semi- circular canals. av = canal between utriculus and sacculus. c = canal between sacculus and cochlea. Coch = cochlea. S = sacculus. U = utriculus. A STUDY OF THE SENSES 311 walled circular membrane which helps to form the partition between the middle ear and the inner ear. Inside of this membrane are two small sacs, the u-tric'u-lus (Latin utric- ulus = a little skin bottle), and a still smaller, sac'cu-lus (Latin sacculus = a small sac). From the utriculus run off three delicate semicircular canals. When we are stand- ing erect, one of these canals in each ear lies in a hori- zontal position, the second is vertical and runs anteriorly and posteriorly, while the third, also vertical, extends from side to side. At one end of each canal is a little swelling, to which runs a branch of the auditory nerve, and other branches supply portions of the walls of utriculus and sacculus. The cells with which these fibers connect are long and slender, and from each projects into the endo- lymph a fine hair. Hence, these cells resemble some- what the sensory cells which lie within the taste buds (see p. 295). If I were sitting on the deck of a rolling ship, I could tell, even with my eyes closed, in what direction I was being rocked. We become more or less conscious, too, of the ordinary movements of the head without the use of the eyes, and the impulses that give us these sensations prob- ably come from the semicircular canals in the following way. All these canals and their enlargements, together with the utriculus, are surrounded by perilymph, and, as we have said, they are filled with endolymph. When the head is moved in any direction, for instance, in walking, the liquid endolymph flows against the projecting hairs of the sensory cells, and an impulse is thus started along the auditory nerve. When this reaches the cells of the fore- brain, we become conscious that some change in the posi- tion of the body is taking place. After we have learned to walk, however, we balance our body without any conscious thought, and walking becomes automatic. We may say, then, that the part of the ear we have been describing gives us a knowledge of our position and movements in space. 312 STUDIES IN PHYSIOLOGY The Structure and Functions of the Cochlea. — The most complicated portion of the inner ear is now to be described. FIG. 145. — Diagram of a Cross Section of a Coil of the Cochlea. AN = auditory nerve. CC= central compartment of cochlea filled with endolymph. OC= sensory cells with long projecting hairs. Sc.T and Sc.V= upper and lower compartments of cochlea filled with perilymph. In general form it resembles a small spirally twisted snail shell ; hence its name coch'le-a (Greek Jcochlias = a snail) (see Fig. 142). Every part of this spiral cavity is divided by two A STUDY OF THE SENSES 313 thin partitions into three compartments ; the upper and lower are filled with perilymph, the smaller middle one contains endolymph. The latter portion of the cochlea is directly connected with the cavity of the sacculus, and hence is in communication with the utriculus and semicircular canals. Sensory cells with long projecting hairs are found on the floor of the central cavity, and to these spirally arranged cells run fibers of the -auditory nerve. Sensations of Sound. — When a stone is dropped into a pond, ripples move outward in circular waves over the sur- face, and finally disappear. In a similar manner sound waves are transmitted in all directions from a given body, say a bell that is struck and caused to vibrate. Some of these waves of air enter the tube of the external ear, cause the tympanic membrane to vibrate, and this in turn sets in motion the chain of small bones that reach across the cavity of the middle ear. The movements of the stirrup bone set in vibration the thin membrane to which it is attached, and so the perilymph which lies in the inner ear becomes dis- turbed. Since the perilymph is continuous throughout the cavities of the inner ear, the vibrations which have been set up in the way we have described may be transmitted in all directions throughout the bony labyrinth. It is probable, however, that these waves become most effective as they move up through the coils of the cochlea, and set in motion the thin partitions that inclose the middle cavity. When the endolymph becomes disturbed, it moves the hairs of the sensory cells, and thus an impulse is finally started along the fibers of the auditory nerve. We get sen- sations of sound when the brain cells receive and interpret these impulses. Loudness, Pitch, and Quality. — The various sounds of which we are conscious differ in loudness, in pitch) and in quality. If I tap a bell lightly, I cause its metal to vibrate only a little; the air waves that influence my middle and inner ear are feeble, and I can scarcely hear the sound. 314 STUDIES IN PHYSIOLOGY A hard stroke, on the other hand, results in a loud note. Hence, loudness depends on the amplitude of the vibrations. A coarse violin string that vibrates but 50 to 100 times in a second produces a very low tone ; when the number is 5000 to 10,000 per second, the note is high. The pitch of a tone, then, depends on the frequency of vibrations. The power of different individuals to distinguish tones varies greatly. Some can hear a low note caused by as few as 30 vibrations per second, or a high note of 30,000 vibrations. The movements of the wings of some insects is more rapid even than this high rate ; hence, human beings cannot hear the sounds they produce. With our eyes closed and at some distance from the in- struments we can easily tell the difference between the same note produced by a violin and a piano. This dif- ference is not one of loudness, nor of pitch, but of quality. When a violin or piano string gives forth a sound, the string moves as a whole, and so produces what is called a fundamental tone. At the same time different parts of the string are vibrating more or less independently, and partial or over tones are also produced. Hence, the air waves that are set in motion by a violin string are a result of a funda- mental tone combined with a certain number of overtones; the piano string, on the other hand, while it can give out the same fundamental, cannot produce the same combination of overtones as does the violin. CHAPTER XV A STUDY OF THE VOICE AND OF SPEECH The Vocal Organs of Man. — Articulate speech is one of the most distinguishing characteristics of mankind — indeed, we may say that man is the only animal that talks. As we might expect, a rather delicate and complicated mechanism is necessary for the production of all these various sounds. This consists of three parts : namely, the lungs, which serve as an air bellows ; the vibrating membranes known as the vo'cal cords (Latin vox, vocis = voice) ; and the resonating chambers of the throat, nose, and mouth chambers. We have already discussed (p. 213) the structure and action of the lungs. We shall now proceed to a description of the voice box or lar'ynx, which contains and regulates the vocal cords. The Cartilages of the Larynx.1 — In our study of the air passages leading to the lungs, we learned that the windpipe is kept open by the C-shaped bands of cartilage, which we can feel on the ventral surface of the neck region. Crowning the windpipe and opening into the throat cavity is the larynx, the walls of which are composed of movable pieces of carti- lage. The largest of these is the thy'roid (Greek = shield- shaped), which can be felt on the ventral surface of the larynx or "Adam's apple." The two halves of the thyroid are partly united on the ventral surface, curve around the sides, but leave a considerable opening dorsally. Each half sends 1 Most of the structures described in this and the following section can be demonstrated to the class by using the windpipe and larynx of a sheep. 315 316 STUDIES IN PHYSIOLOGY out from its dorsal border an anterior projection (which be- comes connected with the hy'oid bone at the base of the tongue) and a posterior process. The two latter processes fit into little sockets in a second cartilage of the larynx, known as the cri'coid (Greek = ring- shaped). The latter surrounds the posterior portion of the larynx and has the form of a signet ring. The flattened part of this band of carti- lage projects anteriorly between the dorsal edges of the thyroid. At- tached to the top, outer corners of this region of the cricoid are two other small pieces of cartilage, each known as a-ryt'e-noid (Greek = ladle- shaped). All of these larynx car- tilages are movable on each other, and this, as we shall see, is a device for regulating the length of the vocal cords and the distance between them. The Vocal Cords. — The larynx, like the throat cavity and the wind- pipe. is lined with mucous mem- Fia. 146. —The Larynx and * J Windpipe, Ventral View, brane, which presents an even sur- face except in the region near the opening into the throat. Here the lining of the voice box is pushed inward to form two rather thick folds, the vocal cords. The latter 6, 6' = bronchi. c = cricoid cartilage. e = epiglottis. h = hyoid bone. t, t' = thyroid cartilage. tr = windpipe. are not like strings, as their name implies; rather, they look and act much like projecting lips. The ventral end of each fold is attached to the inner surface of the thyroid cartilage, and behind or dorsally each is fastened to one of the arytenoids (Fig. 147). During ordinary breathing the two arytenoids are pulled A STUDY OF THE VOICE AND OF SPEECH 317 apart by small muscles, and a V-shaped opening of consider- able size is thus left between the vocal cords. Air then passes inward or outward through the larynx without caus- ing any sound. When, however, we wish to use the voice, in singing or in speaking, the two arytenoids are pulled close together by certain muscles of the larynx, and so only a narrow space is left between the cords. Since the thyroid can rock backward and for- ward (by means of its lower pegs) on the cricoid, other sets of muscles pull the arytenoids and, the thyroid apart from each other, and by this means the vocal cords are tightened. We then force air outward from our lungs, the membra- nous cords are made to vibrate, and a sound is produced. Resonating Cavities. — If a violin string is tightly stretched across the corner FIG. 147.— The of a room and is then set in motion, the resulting sound can scarcely be heard. But when a violin is played, the volume of air inclosed by its thin wooden walls is made to vi- brate as well as the string, and the loudiiess of the sound is thus greatly increased. In a similar manner the sound of our voice depends largely on the vibrating columns of air in the throat, mouth, and nose. Certain bones of the skull have hollow walls, too, which increase the sound produced by our vocal organs. Speech. — The words of which spoken languages are com- posed consist of series of vowels and consonants. The Glottis, from above. viewed Ary — arytenoid cartilages. Arp = muscles between arytenoids. Cal, Cap = muscles from ary- tenoids to cricoid cartilages. Cr = cricoid cartilages. Th = thyroid cartilage. V= vocal cords. 318 STUDIES IN PHYSIOLOGY vowels are a, e, i, o, and u, and these different sounds are produced by altering the shape of the mouth cavity through movements of the lips and cheeks. In none of these sounds does the tip of the tongue touch the palate, the teeth, or the lips. Many of the consonants, on the other hand, are pronounced when the tongue is moved against cer- tain regions of the walls of the mouth. Thus, when we utter t, d, th, or n, the tongue tip presses against the front teeth and hard palate ; these consonants are, therefore, called lin'gu-als (Latin lingua = tongue). In articulating 5, p, and ra we press the lips together, and for this reason we speak of these consonants as la'bi-als (Latin labium = HP). Loudness, Pitch, and Quality. — The loudness of the voice depends upon the force with which the vocal cords and the resonating air columns are made to vibrate. In whispering, faint noises are produced by the escaping air as it is forced through the glottis and mouth opening. The vocal cords do not vibrate when we whisper. When a high note or tone is produced, the vocal cords are stretched tightly and made to vibrate rapidly. Hence, as is the case in other instruments, the pitch of the voice corre- sponds to the rapidity of the vibrations. If we feel of the larynx when uttering a high note, we become conscious that it has risen a little toward the throat. By this means the resonating chamber becomes shorter, and so its rate of vibration can be quickened by the air which is forced from the lungs. In early life the resonating chambers and the larynx are smaller, and the vocal cords are shorter than in later years ; for these reasons the pitch of a child's voice is higher. During the period from thirteen to sixteen years, especially in boys, the rate of growth in this region of the body is very rapid, and so, after "the voice has changed," its tone becomes deeper. The distinguishing quality of an individual voice depends on the combinations of fundamentals and overtones. While A STUDY OF THE VOICE AND OF SPEECH 319 this is largely a result of the size, shape, and relative posi- tions of the air passages, much can be done to improve the clearness and intensity of the voice. The Care of the Voice. — "A pleasing speech and voice are almost equal to personal appearance in importance to the individual in his relations to others. A great number of complex movements are needed to produce proper speech, and these are acquired slowly and with difficulty. . . . Speech is largely the result of imitation, and if the voices a child hears are harsh or coarse, so will his own become. The best way, therefore, to teach a child distinct and re- fined speech is to let it hear such only. However, this is not always all that is sufficient. Enlarged tonsils and, still more, adenoid vegetations block the way of the sound waves to the nasal cavities after they leave the larynx. This deprives the voice of both intensity and resonance. . . . The number of people that are allowed to grow up handi- capped by hasty, slurred, harsh, disagreeable speech and voice is great. Parents do not seem to appreciate the advantage to their children in after life that a refined, melodious voice will be. "Proper singing is one of the best modes of cultivating a pleasant speaking voice, even if the singer has no chance of anything more than a place in a chorus. It is a delight to hear a good singer speak, and often we can tell that a per- son is a singer simply from the speech. . . . When a child's voice is changing, singing should be prohibited until the adult type of voice has been fully developed. This is true of girls as well as boys. Singing is an excellent form of respiratory gymnastics, and tends to develop a full, well- formed chest. In this way it acts as a preventive of lung diseases." — PYLE, " Personal Hygiene" (W. B. Saunders & Co.). Sounds produced by Other Animals. — The song of some birds is most remarkable in its variety and richness. We should, therefore, expect a highly developed larynx. Such 320 STUDIES IN PHYSIOLOGY is not the case, however, for the music of birds is produced in a special organ, the syr'inx (Greek, meaning a pipe), which is found where the lower end of the windpipe divides to form the bronchi (Fig. 146). Here the air tubes enlarge, and the cartilage rings extend little more than half around the windpipe and the bronchi. Tense membranes complete the wall of the air tubes, on their inner side, and act as resonators. Within these tubes are several transverse mem- branes which are vibrated much like the vocal cords of man. The trilling note of certain birds is probably produced by the movements of a semilunar membrane stretched around the sides of the lower part of the windpipe. The croaking of frogs is produced by vibration of vocal cords at the sides of the glottis opening, and the volume of the sound is largely increased by the resonating cavities formed by the lungs and the croaking sacs. The latter open near the angle of the jaws on either side. Most reptiles and fishes produce no vocal sounds whatever. Among the group of insects one finds many different methods of producing noises. None of these, however, can be called vocal, for they are not produced by organs which resemble at all a larynx. Flies, mosquitoes, and many other insects produce a sound by the rapid movements of their wings ; grasshoppers scrape the rough edges of their wings together; while the cicada has a very complex organ on each side of its body by which it produces its deafening clatter. INDEX All figures refer to pages. A * before a figure (for example, *310) indicates an illustration on the page named. A letter n after a figure (for example, 37 n) refers to a footnote on the page named. Abdominal cavity, 92, 144. Abducted, 181. Abomasum, *115, 116. Absorption, 101, 104. adaptations for, 94, 95. Abstinence, arguments for, 70. Accidents to skeleton, 184. Accommodation of eye, *303. Acids, test for, 14. Adam's apple, 85, 210, 315. Adaptations, of food to individual needs, 107. shown in skull, 172. shown in spinal column, 166. Adducted, 181. Afferent nerves, *258, 264, *266. Air, amount of, 6. changes due to respiration, 222. composition, 10, 14, *15. how lungs are filled with, 218. passages, 85, *211. pressure, 11, 12. sacs in lungs, 211, *215 study of, 11-15. Albumin, see Proteids. Albuminous substances, see Pro- teids. Alcohol, as a stimulant, etc., 66-74. composition, 66 n. danger in use of, 69, 109. effect on circulation, 154. effect on dogs, 71-74. effect on digestion, 109. effect on nervous system, 285. effect on temperature, 243. in patent medicines, 39. life insurance and, 70-71. preparation of, 36. Alimentary canal, absorption from, 101—104. of bird, *114. of earthworm, *112. of frog, *113. of sheep, *115. parts of, 75, *76. Ammonia, 44. Amoeba, 23, *24. cell division, 30, *31. locomotion, 205. nervous functions, 287. nutrition in, *117. respiration of, 229. Amphibia, see Frog. corpuscles of, *126. skin of, 244. Anaemia, 124. Anatomy, 2. also see Alimentary canal of bird, earthworm, reptile, etc. Ankle joint, 181. Anterior, 20. Antitoxin, 224. Antlers, 247. Anvil (incus) bone, *309. Aorta, 134, *143, *145. Aortic arches, *112, 154. Apex of heart, 130. Appendages, 20, 21. Appendicitis, 96. Appendix, vermiform, *76, 96. Aqueous humor, 302. Arachnoid, 257, 273. Arm, skeleton of, 160, *163. control of movements, 280. of child, 173. Arterial blood, 147. 321 322 INDEX Arteries, see Aorta, Carotid, etc. Artery, 129, 137. effect of heat and cold on, 151. structure of, *137. Articular processes, *165. Artificial respiration, 225. Arytenoids, cartilages, 316, *317. Ascending colon, *76, 96. Assimilation, 29. Astigmatism, 306. test for, *306. Atlas vertebra, *166. Atmosphere, pressure of, 6. Atwater, Prof. W. O., 42 n, 66. Auditory nerves, of frog, 269. of man, 279, *307, 310. Auricle, *130, 131, *132. Axis vertebra, *166. cylinders, 285, 258. Bacillus tuberculosis, 224. Backbone, see Spinal column. Bacteria, *32-33. changes caused by, 32. conditions for growth, 34. reproduction of, 34. study of, 32-35. Ball-and-socket joints, 180. Bathing, 240. Baths, 240-241. Bats, locomotion of, 207. Beat of heart, 134. Beef blood, 118-121. Belly of muscle, 195. Biceps muscle, *194. Bicuspid (premolar) teeth, 78. Bile, 99. duct, *76, 99. Biology, 3. Birds, alimentary canal, *114. brain of, *289. circulation of, 157. feathers of, *245. locomotion of, 207. respiration of, 230. skeleton of, 189. skin of, 245. song of, 319. syrinx of, 320. Bladder, urinary, 240. Blood, corpuscles of, 23, *25, 26. manufacture, 75-116. Blood, corpuscles of — Continued. plasma, 26. regulation of supply, 148. serum, 127. study of, 117-128. vessels, 129, 137-142. Blood supply, to bones, 176. dermis, *234, 235. epidermis, 233. hair, 237. heart, 136. kidneys, *250. lungs, *215. mucous membrane, 77. muscles, *198. Blushing, 280. Body, as a machine, 2. chemical composition, 16. of vertebra, 165. regions of, 20. Boiling meats, 53. vegetables, 55. Bones, 23, *27. structure of, 174-176. study of, 159-192. Bony framework, uses of, 159. Botany, 4. Brain, 21, *254. of frog, 268-273. of man, 273-283. Bread, composition of, 41. making of, 56. Breastbone (sternum), 168, *173. of child, 173. Broiling meats, 54. Bronchial tubes, 211. arteries, 215. Bronchitis, 223. Bronchus, *211. Bruises, treatment of, 153. Budding of yeast, *27.. Burning, see Oxidation. Burns, treatment of, 242. Cfficum, *22, *76, 96. Calomel, 100. Calorie, 51. Calorimeter, 51. Camera, eye as, 303. Canine teeth, 78. Capillaries, 129, 138-*141. of frog's foot, 141. INDEX 323 Carbohydrates, 17. amount needed per day, 56. presence in vegetable food, 47. used in proteid manufacture, 50. uses of, 51. Carbon, in carbohydrates, 17. in fats, 17. in proteids, 18, 50. in starch manufacture, 47. properties of, 7. Carbon dioxid, composition, 9. given off by lungs, 210. in starch manufacture, 48. preparation of, 7. produced in body, 16, 17, 18. produced by yeast, 36. properties, 8. removal from body, 19, 210. symbol, 9. test for, 8, 16. Cardiac orifice, 88. Care of voice, 319. Carotid artery, 143. Carpal bones, 160. Carron oil, 242. Cartilage, *27. of larynx, *315. of windpipe, *214. Cells, 23, 25, 26, *28, 39. as units of living substance, 23-32. division of, 30. of bacteria, *32. of leaf, 48. of spinal cord, *258. of yeast, *37. Cellulose, 25. in bacteria, 33. Cement substance, 80. Centrum of vertebra, 165. Cerebellum, comparison of, *290. of frog, 269. of man, 275. Cerebral hemispheres, comparison of, 289. of frog, 268, 272. of man, 274. Cerebro-spinal fluid, 257. nerve center, 254. Cervical enlargement, 256. nerves, 261. vertebra, 162. Changes due to respiration, 231. in blood, 147. Cheek bones, 171. Chemical composition, of air, *15. alcohol, 66 n. blood, 127. body, 16-19. bones, 177-178. glycogen, 17 n. grape sugar, 17 n. hemoglobin, 18 n. inspired and expired air, 221- 223. protoplasm, 28. Chemistry, 4, 16. Chest cavity, 216-220. Child skeleton, 172-174. nervous system, 283. Chlorate of potassium, 11,, Chlorophyll bodies, 48. Choking, 225. Chordae tendinese, 132. Choroid coat, 300. Cicada, noise of, 320. Cilia, 33, 206. in windpipe, 213, *214. Ciliary muscle, 302. Circulation of the blood, 129-158. Circumducted, 181. Circumvallate papillae, 295. Classification, of bones, 176. joints, 180. Clavicle, 169. Claws, 247. Clot of blood, 118. Clothing, kinds of, 242-243. and respiration, 223. Coagulation of blood, 119, 121. Coats of the eye, 300-302. Coccygeal nerves, 261. Coccyx, 165. Cochlea, 312-313. Coffee, 64. Colds, 152, 223. Collar bones, 169. Colloids, 103. Colon, *76, 96. Colony, of bacteria, 33. of yeast, 38. Color blindness, 307. of blood, 125. Commissure of cord, 258. 324 INDEX Comparative study, of blood, 125- 127. circulation, 154-158. digestion, 109-116. excretory organs, 251—252. locomotion, 205-208. nervous system, 287-290. respiration, 229-231. skeleton, 186-192. skin, 244-247. Compounds, 9. Connective tissues, 23, *180. Conscious activities, 280. Constipation, prevention of, 108. Consumption, 224. Convolutions, 275, 290, *274. Cooking of food, 52-56. Cooperation of organs, 253. Coral, *186. Coronary arteries, 137. Corpuscles of blood, *25. red corpuscles, *25, 26, *122, *126. white corpuscles, 26, 122, 126. tactile, 235, *291. Cortex, of brain, 276. of kidney, 249. Coughing, 225, 280. Cranial nerves, of frog, 269. of man, 278-279. Cranium, 170. Crayfish, *188. green glands of, 252. Cribiform plate, 296. Cricoid cartilage, 316. Croaking sacs of frog, 320. Crop, of bird, 115. of earthworm, 113. Croup, 223. Crown of tooth, 79. Crystalline lens, 302. Crystalloids, 103. Cuts, treatment of, 153. Dandruff, 241. Danger in use of alcohol, 69. Daughter cells, of amoeba, 31. of yeast, 38. Defibrinated blood, 120. Dental formula, 79. of dog, 111. of horse, 111. Dental formula — Continued. of milk set, 79. of permanent set, 79. of rabbit, 110. Dentine, 80. Deoxygenated blood, 148. Dermis, 235-236. Descending colon, *76, 96. Diaphragm, 21, *211. movements of, 216. of rabbit, *22. Diet, 56-57. Digestion, 75. hygiene of, 106-109. in intestines, 93. of fats, 97-98. of insoluble salts, 91. of proteids, 91, 97. of soluble salts, 84. of starch, 84, 97. of sugar, 84. synopsis of, 105. Digestive glands, 75. Diphtheria, 223. Disease germs, 35. Dislocations, 185. Distillation, 36. Distilled liquors, 39. Division of cell, 30. Dog, brain of, 289. dental formula, 111. Dorsal, 21. horns of gray matter, *258. nerves, 261. roots of nerves, 261, 264. vertebrae, 162. Ducts of plants, 47. Dura mater, 257, 273. Dusting, 228. Ear, 308-314. drum, 308. wax, 308. Earthworm, *112. alimentary canal, 112. circulation, 154. excretion, 252. locomotion, 206. nervous system, 287. respiration, 229, 230. Eating, hygienic habits of, 106. Economy of foods, 57-60. INDEX 325 Efferent nerves, *258, 264, *266. Elements, 8, 9. Emulsion, 97. Enamel of tooth, 79. Endolymph, 310, 311. Energy, production of, 29. Engine, compared to body, 1, 29. oxidation in, 17. Epidermis, 233-235. Epiglottis, 85. Esophagus, *85, 87. Ethmoid bone, 170, 296. Eustachian tubes, 86, 309. Excretion, 251. Exercise, effect on blood, 123. circulation, 152. muscles, 203. respiration, 222. Expiration, 209, 219. Extend (joint), 181. Extensor muscle, 195. External ear, 308. Eye, 298-307. lids, 299. Face, bones of, 171. Fang of tooth, 79. Far-sighted eyes, 306. Fats, absorption of, 95, 100. amount in body, 17. amount needed each day, 56. digestion of, 97-98. effect of heat on, 17. in protoplasm, 28. test for, 44. uses of, 17, 51. Fehling's solution, 45 n. Femur, 162. Fermentation, 37. Fibers, of muscle, 198. of nerves, *259. Fibrin, 119. Fibrinogen, 120. Fibula, 162. Filiform papillae, 294. Fish, brain of, 289. circulation, *155. locomotion, 207. respiration, 229, skeleton, 188. skin of, 244. Fissures, 256. Fissures — Continued. of Rolando, 275. of Sylvius, 275. Flat bones, 177. Flex (joint), 181. Flexor muscle, 195. Flies, noise of, 320. Focus on retina, 304. Fontanelle, 172. Foods, 41. adaptation to individual needs, 107. alcohol as a, 66-68. and muscles, 202. and nervous system, 284. and skeleton, 182. composition of, 41—44, *43. cooking of, 52—56. economy of, 57—60. nutrients in, 41, *43. refuse in, 42. uses of, in body, 30, 41. Foramen magnum, 170. Forebrain, of frog, 268. of man, 275. Fractures, 184. Frog, alimentary canal, *113. brain of, *269. circulation of, *156. corpuscles of, *125. croaking of, 320. flow of blood in foot, *141. locomotion of, 207. nervous system, 268-273, 289. respiration, 229. skeleton of, *189. skin of, 244. Frontal bone, 170. lobes of brain, 275. Fuel value of nutrients, 51. Function, 21. of all protoplasm, 40. Fungiform papillae, 294. Gall bladder, *76, *99. Ganglion, 262. of brain, 276. of sympathetic nervous sys- tem, 266. Gastric artery, 144. glands, *88. juice, 88. 326 INDEX Gelatin, 53. General senses, 293. Girdles of skeleton, 168-170. Gizzard, of bird, 115. of earthworm, 113. Glands, digestive, 75. gastric, *88. of the skin, 238. salivary, 82. Gliding joints, 182. Glosso-pharyngeal nerves of frog, 269. of man, 279. Glottis, 210. Glycerin, 97. Glycogen, 17, 100. composition and symbol, 17 n. Gray matter, 258. Grape sugar, 17. composition and symbol, 17 n. test for, 45. Grasshopper, noise of, 320. Gristle, see Cartilage. Growth, 29. Gullet, see Esophagus. Gums, 77. Habits, 282. of breathing, 222. of eating, 106. Habitual activities, 281. Hair, 232, 236-238, *237. care of, 241. of mammals, 247. Hammer (malleus) bone, *309. Hangnails, 241. Hard bone, 175. palate, 77. Haslet, 213. Head, skeleton of, 170. of bones, 175. Hearing, sense of, 308-314, 380. Heart, 21, 129-137. . and lungs, *130. muscle, *202. of rabbit, *22. Heat regulation, 239. Hemoglobin, composition of, 18 n. use of, 122. Hepatic artery and vein, 146. Hilum of kidney, 248, *249. Hindbrain, 268. Hindbrain — Continued. of frog, 269, 271. of man, 275. Hollow bones, advantage of, 176. Hoofs, 247. Horns, 247. of gray matter, 258. Horse, skeleton of, *190. foot of, *191. locomotion of, 208. Humerus, 160. Humors of the eye, 302. Hunger, sensations of, 294, Hydrochloric acid, 89. action on bone, 178. Hydrogen, in carbohydrates, 17. in proteids, 18. oxidation of, 10. Hygiene, of blood, 123-124. of circulatory system, 151—154. of digestion, 106-109. of the eyes, 307. of muscles, 202-205. of nervous system, 283-286. of respiratory organs, 222—228. of skeleton, 182-184. of skin, 240-243. of voice, 319. Hyoid bone, 316. Ilio-co3cal orifice and valve, 96. Impulses (nervous), 264. Incisor teeth, 78, 80. Incus bone, 309. Inferior vena cava, 133, 144, *145. Inner ear, 310. Insects, noises of, 320. Insertion of muscle, 195. Inspiration, 209, 219. Intemperance, cost of, 71. Intercellular substance, 27. Inter vertebral foramina, 168, 260. Intestines, 21, *76, 92-96. absorption in, 104. of mouse, *94. of rabbit, *22. Invertebrates, 20. classes of, 20. kidneys of, 252. nervous system of, 288. skeleton of, 187. skin of, 244. INDEX 327 Involuntary muscle, 90, 194, 201, *202. Iodine, solution, 45 n. symbol, 9. Iris of the eye, 301. Iron in hemoglobin, 18 n. symbol, 18 n. Irregular bones, 177. Jaundice, 99. Jawbones, 171. Joints, 179-182. Jugular veins, 144. Kidneys, 21, 248-252. excretion of urine, 18. Kinds of muscle, 193. Kneecap, 162. Labial consonants, 318. Lac teals, *95, 151. Large intestines, *76, 96. Larynx, 210, 212, 314. of birds, 319. Lateral processes of vertebra, 165. Laws, pure food, 46. Leg, bones of, 162. movements of, 281. of child, 174. Lens of the eye, 302, *303. Life insurance, 70-71. Ligaments, 179. Lime water, as test for carbon di- oxid, 8, 210. preparation of, 8 n. Lingual consonants, 318. Liquors, distilled, 39. malt, 38. Litmus paper, 14. Liver, 21, 98, *99. as an excretory organ, 252. glycogen in, 17. of rabbit, *22. Living substance, see Protoplasm. Localization of functions in brain, 280-281. Locomotion, comparative study, 205-208. Locomotive, see Engine Long bones, 176. Loudness of sound, 313, 318. Lumbar enlargement of cord, 256. nerves, 261. vertebra?, 162. Lungs, 21, 213-216. as excretory organs, 251. of rabbit, *22. Lunula, 236. Lymph, 148-149. Lymphatic nodes, *151. system, 148-151. Lymphatics, *149. Malar bones, 171. Malleus bone, 309. Malt liquors, 38. Mammals, 247. anterior appendages of, 190^ Mandible, 171. Marrow, 175. Match, study of, 5-10. Meats, composition of, 42. cooking of, 52—54. Medicines, patent, 39. Medulla oblongata, comparison of, 290. of frog, 269. Medullary region of kidney, 248. sheath, 259, 283. Memory, 280. Mesenteric arteries, 144. Mesentery, *93. Metabolism, 30. Metacarpal bones, 160. Metatarsal bones, 162. Miclbrain, of frog, 268, 271. of man, 275. Middle ear, 309. Mineral substances, amount in body, 16. digestion of, 84, 91. test for, 8, 46. uses of, 52. Mitral valve, 132. Molar teeth, 78. Mosquito, noise of, 320. Motor cells and fibers, 278. Mouth cavity, 77, *81. absorption in, 103. Mucous membrane, 77. Mucus, 77. Muscles, 23. of esophagus, 87. 328 INDEX Muscles — Continued. of eyes, 299. of intestine, 93. of stomach, 90. of tongue, 82. study of, 193-208. Nails, 232, *236. care of, 241. Narcotics, 63. Nasal bones, 171. " cavities, 296. Near-sighted eyes, 306. Neck of tooth, 80. Nerve centers, 254, 262. cells, *259, 263, 277, (of child), 283, number of, 284. fibers, *259, 263-264. impulses, 264, 277. trunks, 254. Nerves, 23, 256. of frog, 269-270. of hair, 237. of muscles, 199. of skin, 235. of stomach, heart, etc., 267. spinal, 260-266. Nervous system, 253, 290. Neural arch, 165. ring, *165. Nitric acid, 44. Nitrogen, amount in air, 24. in nitrogenous substances, 18. preparation, *13. properties, 15. use in air, 15. Nitrogenous substances, see Pro- teids. Noises of insects, 320. Nosebleed, 153. cavity, 211, 297. Nucleus, 25. Nutrients, 41. fuel value, of, 51-52. in various foods, *43. tests for, 44. uses of, 50-52. Nutrition, in amoeba, 117. in man, 117. Occipital bones, 170. convolutions, 280. Oil glands, 238. Olfactory lobes and nerves, of frog, 268. of man, 275, 289. comparison of, 290. region of nose, 297. Optic lobes and nerves, of frog, 268. of man, 275, 279, 300. comparison of, 290. Organism, 39. Organs, 21, 39. of plants, 47. Origin of muscle, 195. Osmic acid, 44 n. Osmosis, 101-103. Oxid, of carbon, 7. of hydrogen, 7. of manganese, 11. of phosphorus, 5, 13, 14. of sulphur, 7. Oxidation, 10. in body, 16, 17, 19, 29, 50, 51 of alcohol, 66-68. of carbon, 7, 8. of fats in the body, 17. of phosphorus, 6. of sulphur, 7. Oxygen, amount in air, 14. effect on blood, 121. in carbohydrates, 17. in proteids, 17. in starch manufacture, 48-49. preparation, *11. properties, 12. use in air, 13. use in body, 16, 17. Oxygenated blood, 147. Pain, sensations of, 293. Palate bones, 171. hard, 77. soft, 77. Pancreas, 21, 97-98. Pancreatic juice, 97. Papillae, of dermis, 235. of tongue, 82, 294. Papillary muscles, 133. Paramecium, 205. Parietal bones, 170. Parotid glands, 82. Patella, 162. INDEX 329 Patent medicines, composition of, 39. use of, 108. Pectoral girdle, 169. Peculiarities of human skeleton, 192. Pelvic girdle, 170. bones, 170. Pelvis of kidney, 248. Pepsin, 89. Peptone, 91. Pericardium, 130. Perilymph, 310. Perimysium, 197. Perineurium, 262. Periosteum, 174. Peritoneum, 92. Peritonitis, 92. Perspiration, 239. Perspiratory glands, 238. Phalanges, 160, 162. Phosphorus, 5, 13. Physical properties, 12. Physics, 4. Physiology, 3. Pia mater, 257, 273. Pigment spots, 235. of eye, 301. Pitch of sound, 314, 318. Pivot joints, 182. Plants, cells of, 25 n. manufacture of food by, 47. organs of, 47. Plasma of blood, 26, 120. Pleura, 216. Pleurisy, 225. Pneumonia, 223. Poison, 62. alcohol as a, 69. Pons Varolii, 275. Pores of sweat glands, 223. Portal system, 145. Posterior, 21. Premolar teeth, 78. Pressure, on bones, 183. of the atmosphere, 12. Primitive sheath, 259. Processes of vertebrae, 165. Proteids, 18. amount needed each day, 56. digestion of, 91, 97. in protoplasm, 28.. Proteids — Continued. manufacture of, by plants, 50. tests for, 44. uses of, 50. Protein, 42 n. Protoplasm, 25, 39. chemical composition of, 28, 50, 51. functions of, 40. properties of, 28—32. Proventriculus, 115. Psalterium, 116. Ptyalin, 84. Pulmonary artery, 133. • circulation, 142. veins, 134. Pulp cavity, 81. Pulse, 137. absence in capillaries and veins, 141. Pupil of eye, 300. Pure food laws, 46. Pus, 122. Pylorus, 88. Pyramids of kidney, 248. Quality of sound, 314, 318. Rabbits, organs of, *22. teeth of, 110. Racemose glands, 83, 97. Radial artery, 144. Radius, 160. Rectum, *76, 96. Reflex action, 265, 278. Refuse of foods, 42. Renal arteries, 144, 250. veins, 250. Rennin, 89 n. Repair in body, 29. Reproduction, of amceba, *31. of bacteria, 33. of yeast, 37. Reptiles, brain of, *289. ' circulation of, 157. locomotion of, 207. skin of, 244. Resonating chambers, 315, 317. Respiration, 209-231. calorimeter, *55. Respiratory region of nose, 297. Rest, necessity of, 204, 285. 330 INDEX Reticulum, *115. Retina, 302. Ribs, 168. movements of, 174. structure of, 174. Ridges on skin, 233. of intestine, 94. Roasting meats, 54. Rolando, fissure of, 275. Root of tooth, 79. Rotated, 181. Rumen, *115. Running, 200. Sacculus, 311. Sacrum, 162. Saliva, 82. Salivary glands, 82-84, *83. Saponification, 97. Scapula, 169. Sclerotic coat, 300. Sebaceous glands, 238. of eye, 299. Second wind, 222. Secretion, 251. Semicircular canals, 311. Semilunar valves, 133. Sensations, of hunger and thirst, 294. of pain, 293. of sight, 304. of smell, 297. of sound, 314. of taste, 295. of temperature, 293. of touch, 292. Senses, 291-314. general, 293. of hearing, 308, 314. of sight, 298-307. of smell, 296-298. of taste, 84, 294-296. of touch, 291-293. Sensory cells and fibers, 278 hairs of ear, 313. hairs of nose, 297. Serous membrane, 131. Serum, 119, 120. hygiene of, 124. Shaft of bones, 175. Shedding of teeth, 79-80 n. Sheep, alimentary canal of, *115. Sheep — Continued. kidney of, 248. Short bones, 177. Shoulder blades, 169. Sight, sense of, 280, 298-307 Sigmoid flexure, *76, 96. Singing, 319. of birds, 319. Sylvius, fissure of, 275. Skeleton, 159-192 ; see Birds, Frog, etc. Skin, 232-247. Small intestine, *76, 92-95. absorption in, 104. Smell, sense of, 296-298. Snakes, locomotion of, 208. fangs of, 110. ribs of, 188. Sneezing, 225, 280. Soap, 97. Soft palate, 77, 84, *85. Solar plexus, 267. Sounds of the heart, 136. Soups, 53. stock, 178. Speech, 317. Sphenoid bone, 170. Sphincter (pyloric), 88. Spinal column, 162-168. of child, 173. Spinal cord, of frog, 270-271. of man, 21, 256, 260. Spinal nerves, of frog, 270. of man, 260-266. Spinous processes, 365. Spleen, 21. Splenic artery, 144. Spongy bones, 171. bone tissue, 175, 296. Spores, 34, 38. Sprains, 185. Standing, 199. Stapes bones, *309, 311. Starch, digestion of, 84, 97. manufacture of, in plants, 47, 48 n. storage of, 49. test for, 45. Starfish, *187. Sternum, 168. Stewing meats, 54. Stimulants, 62. INDEX 331 Stirrup bone, 309, 311. Stomach, 21, *87, 88-92. absorption in, 104. of rabbit, *22. Stomata of leaves, 48. Striped muscle, *198. Structure of animal bodies, 20-21. Sublingual glands, 83. Submaxillary glands, 83. Suffocation, 225. Sugar, digestion of, 84. in protoplasm, 28. Sulphur, 6. Superior vena cava, 133, 144, *145. Suspensory ligaments, 302, *303. Sutures, 172. Swallowing, 85, 86, 87. Sweat glands, *237, 238. Sweeping, 227. Sympathetic nervous system, of frog, 269. of man, 201, 266, 268. Synovial membrane and fluid, 180. Syrinx, 320. Systemic circulation, 142. Tactile corpuscles, 235, 291. Tarsal bones, 162. Taste buds, *295. sense of, 84, 294-296. Tea, 63. Tear bone, 171. glands and duct, 298, *299. Teeth, human, 77-81. care of, 107. comparative study, 109-111. Temperature of blood, 125. effect of alcohol on, 243. regulation of, 239. sensations of, 293. Temporal bone, 170. convolutions, 280. Tendons, 23, 180. Terminal brush, 259. Tests, for nutrients, 44—46. for carbon dioxid, 8. Thigh bone, 162. Thirst, sensations of, 294. Thoracic duct, *150. Throat cavity, 84-86, 272. absorption in, 104. Thyroid cartilage, 315. Tibia, 162. Tissue, 23, 28, 39 ; see Bone, Carti- lage, Muscle, etc. Tobacco, 64. Tongue, in man, 81—82. in other animals, 111. Tortoise or turtle, 245. Touch, 291-293. Toxins, 123, 223. Trachea, *85, *212. Transverse colon, *76, 96. Treatment of cuts and bruises, 153. Triceps muscle, 195. Tricuspid valve, 132. Tuberculosis, 224. Tubules of kidney, 249. Turbinate bones, 171, 296, *297. Tympanum, 308. Ulna, 160. Ulnar artery, 144. Urea, formed in body, 18. given off by kidneys, 249. Ureter, 248, *249. Urethra, 250. Urinary bladder, 250. Urine, 249. Utriculus, 311. Uvula, 81, 84, *85. Vagus nerve, of frog, 269, of man, 279. Valves of heart, 132-136. ileo-coecal, 96. in veins, *138. Vegetables, cooking of, 55. Veins, 129, 138. Vena cava, 133, 144. Venous blood, 147. Ventilation, 226-227. Ventral, 21. horns of gray matter, 258. roots of spinal nerves, 261, 264 Ventricle, 131. Vermiform appendix, 96. Vertebra, 162, *165. Vertebrates, 20. classes of, 20. kidneys of, 252. nervous system of, 288. skeleton of, 186. Villi, *95. 332 INDEX Vitreous humor, 302. Vocal cords, 315-316. organs of man, 315. Voice and speech, 315-320. Voice box, 315. Voluntary muscles, 194-201. Vomer bone, 171. Walking, 200. Wastes of body, 18, 29, 210. given off by kidneys, 249. given off by lungs, 210. of food, 72. Water, amount in body, 16. composition and symbol, 9. given off by kidneys, 249. given off by lungs, 210. in protoplasm, 28. Water — Continued. test for, 7, 46. uses of, 52. Wax glands of ear, 308. White corpuscles, 26, 122, 126. matter of cord, 258. Windpipe, 85, *212. Wisdom teeth, 79. X-ray pictures, 159. Yeast, 35-39, *37. changes caused by, 35. reproduction of, 37. uses of, 38. Yellow spot, 305. Zoology, 4. E following pages contain advertisements of a few of the Macmillan books on kindred subjects A TEXT-BOOK OF PHYSIOLOGY. By MICHAEL FOSTER, M.A., M.D., LL.D., F.R.S., Professor of Physi- ology in the University of Cambridge, and Fellow of Trinity College, Cambridge. 8vo. With Illustrations. Sixth Edition. Largely Revised. PART I. Blood; The Tissues of Movement; The Vascular Mechanism. $2.60. PART II. The Tissues of Chemical Action; Nutrition. $2.60. In the Press. PART III. The Central Nervous System. $1.75. PART IV. The Central Nervous System (concluded) ; The Tissues and Mechan- isms of Reproduction. $2.00. PART V. (Appendix) The Chemical Basis of the Animal Body. By A. SHERI- DAN LEA, M. A., Sc.D., F.R.S. $1.75. " The present edition is more than largely revised. Much of it is rewritten, and it is brought quite abreast with the latest wave of progress of physiological science. A chief merit of this work is its judicial temper, a strict sifting of fact from fiction, the discouragement of conclusions based on inadequate data, and small liking shown toward fanciful though fascinating hypotheses, and the avowal that to many ques- tions, and some of foremost interest and moment, no satisfying answers can yet be given." — New England Medical Journal. " It is in all respects an ideal text-book. It is only the physiologist, who has devoted time to the study of some branch of the great science, who can read between the lines of this wonderfully generalized account, and can see upon what an intimate and extensive knowledge these generalizations are founded. It is only the teacher who can appreciate the judicial balancing of evidence and the power of presenting the conclusions in such clear and lucid forms. But by every one the rare modesty of the author in keeping the element of self so entirely in the background must be appreci- ated. Reviewing this volume as a whole, we are justified in saying that it is the only thoroughly good text-book of physiology in the English language, and that it is probably the best text-book in any language." — Edinburgh Medical Journal. FOSTER'S TEXT-BOOK OF PHYSIOLOGY. In One Volume. 8vo. Cloth, $5.00. Sheep, $6.00. Abridged and revised from the Sixth Edition of the Author's larger work published in five octavo volumes. This new edition contains all the illustrations included in the larger work, and is published in one octavo volume of about 1400 pages. It contains all of the author's more important additions to the complete work, and is like the sixth edition of that copyrighted in this country. PHYSIOLOGY FOR BEGINNERS. New Edition, with an addi- tional Chapter on Alcohol and Food. By MICHAEL FOSTER and L. E. SHORE. Now ready. i6mo. Price, 75 cents. THE MACMILLAN COMPANY 66 FIFTH AVENUE, NEW YORK CONSTIPATION IN ADULTS AND CHILDREN With special reference to Habitual Constipation and its most Success ful Treatment by the Mechanical Methods, by H. ILLOWAY, M.D., formerly Professor of the Diseases of Children, Cincinnati College of Medicine and Surgery; with many plates and illustrations. 8vo. $4.00; sheep, $5.00. " The work is not large, but is replete with facts which are of practical value to the practitioner of medicine." — The Canadian Journal of Medicine and Surgery. ATLAS OF EXTERNAL DISEASES OF THE EYE By A. MAITLAND RAMSAY, Ophthalmic Surgeon, Glasgow Royal Infirm- ary; Professor of Ophthalmology, St. Mungo's College, Glasgow; and Lecturer on Eye Diseases, Queen Margaret College, University of Glasgow. With 30 full-page colored plates, and 18 full-page photogravures. Sold only by subscription. 4to. Half morocco, gilt top. $20.00. " A work of great beauty. The illustrations are unrivalled, many of them master, pieces in their kind. The text gives connected descriptions of the diseases, supple- menting the stages and phases not presented in the illustrations. It is prepared with the utmost care as to precision and comprehensiveness of language. The book is written for the observing student, describing the etiology, symptomatology, and pathology of the diseases, but omitting the treatment. The whole work, which in care of preparation and elegance of getting up, appeals, in contrast with the book of Haab, to a select class of readers, is an ornament to Scotch ophthalmology, and in particular to Glasgow, the place from which emanated the best ' practical treatise on the diseases of the eye ' before the discovery of the ophthalmoscope — the classical text-book of William Mackensie." — H. K., Archives of Ophthalmology, New York, DR. H. KNAPP, Editor. THE FUNDUS OCULI With an ophthalmoscopic atlas illustrating its physiological and patho« logical conditions, by W. ADAMS FROST, F.R.C.S., Ophthalmic Surgeon, St. George's Hospital; Surgeon to the Royal Westmin- ster Ophthalmic Hospital. 4to. Half morocco. $20.00. Sold by subscription only. " A work which is a pleasure to look upon and an equally great pleasure to read. The book is a folio of 220 pages of letterpress, illustrated by 46 figures in black and white, of exquisite workmanship, representing macroscopically and microscopically those parts of the eye which we see with the ophthalmoscope. Bound up in the same volume are 47 large colored plates, containing 107 figures, beautifully drawn and colored, representing the fundus of the eye as seen with the ophthalmoscope. The discussion of the different conditions observed in the fundus bears evidence of very careful observation and research. The direct, concise, and lucid manner in which the descriptions of the various conditions are given is truly admirable." — N. Y. Medical Record. " We venture the assertion that of all Ophthalmoscopic Atlases which have been produced in the last forty years, Mr. Frost's book \s facile princeps. We wish that it might be found in the library of every physician and surgeon." — PROFESSOR JAMES MOORE BALL, Editor The State Medical Journal and Practitioner. THE MACMILLAN COMPANY 66 FIFTH AVENUE, NEW YORK IS DUE ON THF 65537 304679 UNIVERSITY OF CALIFORNIA UBRARY